Adding viable tinkering inventions to your game

[Dalebert]

I've seen this done in a game where the DM allowed a gnome tinkerer to come up with actually useful tinkerings including weapons, but I feel like it went too far. The inventions were TOO good IMHO. An example was a throwing star launcher that shot like d6+1 stars and could hold about 10. It would occasionally jam and waste your action and require further tinkering to fix it. Still, it was about the equivalent in damage to casting a Burning Hands.

I have some notions of tinker items that I think could spice up a game. I want them to be useful but unreliable enough to be kind of discouraging, particularly if you're a control freak unwilling to take chances. Want to add ideas? Please do!

Potion Helmet/Hat (Inspired by the infamous beer hat you've seen at ballgames)
The tinkerer can load 1 or 2 potions upside-down into this device that can be worn by anyone. Tubes lead from the potions to a mouthpiece that can be worn into combat. The wearer can consume a potion with a bonus action by pressing a button on either side of the helment--one for each potion. They must make a DC 8 dex roll to successfully trigger the release. On a 1, the potion squirts out ineffectively and is lost. If they attempt to press the button with a hand that's holding something, the DC becomes 12 and potion loss happens on a 1 or 2.

Flame Gun
The tinkerer must load this gun with a vial of oil or other combustible substance like alcohol. It can then be used by anyone. There is a one-handed version treated as a hand crossbow and a two-handed version treated as a light crossbow. A pump lever on the back must be activated for a full round to pressurize the chamber and a pilot light must be lit which requires another full action. Roll a d20. On a roll of "1", the loading process results in a misfire detailed below. The wielder than has 10 minutes to fire it before too much air has leaked from the chamber. Once prepared, it can be fired to launch flame at a single target within 15 feet dealing 1d6 immediately and another 1d6 at the end of the creature's next turn if it hasn't taken an action to extinguish the flames.
Misfire: On a roll of "1", either when loading or firing, the device springs a leak and the wielder must make a DC 15 dex-save or experience the effect instead of the target.

Grappling Gun
This is essentially a modified light or heavy crossbow but it fires a modified grappling hook with a special fine cord attached. It takes a full minute to prepare it for firing and the range for either device is 25/50. This cord is not as strong as a regular rope and there is a 10% chance it breaks if more than 100 lbs of force is applied to it. It can be used to aid in climbing but an alternate use is as a weapon. If successfully fired at an enemy, it embeds itself in their flesh. If the target or an ally does not spend an action to remove it, the wielder may then use an action to pull the cord and deal another 1d4+str bonus damage. Do a str vs. str check. If the wielder succeeds, the target is pulled 10 feet toward him and it remains in their flesh allowing them to do it again on a following action. Otherwise the hook pulls free.
Jam: On a roll of "1", the device malfunctions and requires tinkering to repair.

[JellyPooga]

A good rule of thumb would be to compare any potential tinkering to Cantrips. If it's blatantly more powerful than a Cantrip, it's a no-go.

A device that replicates anything Prestidigitation, Druidcraft or Thaumaturgy can do is fine.

Something that replicates an Eldritch Blast cast by a 20th level Caster or the equivalent of any 1st level spell; not so much.

Anything in-between? Case-by-case basis.

[zylodrizzt]

Spring loaded boots
Use a move action to activate launching u straight in a direction of your choice takes an action to reset. Until you reset them your speed crops by 10 ft.

Walkie talkie
You create a pair of speaking devices that can be used at a distance to speak through other walkie talkie. This mimics the can trip message however it can be heard 60ft away. This effect can be used 6 times a day split between devices.

You know I was thinking instead of penalties (in some cases they make sense) why not just only allow limited access like on a short or long rest where long rest would have a number of uses. Or maybe like charges where you run out n then its totally unusable even for parts possibly exploding on you. Or mimic effects (in a limited fashion) of things others could do at similar levels like bm manuvers or can't trips none of which scale with level possibly cropping any five rolled by a size or reduced distance or effect depending. What I think?

[Joe the Rat]

A popular one for my bunch are continual flame lamps with irising shutters. Flipping a switch or twisting the rim to open/close. We've had this in headlamp and, er... "headlight" configurations. The light part is magical in this case, but you could do something similar on a standard lamp, or a candle-lamp.

I've also been contemplating spring driven spools and pulleys. Wind it up now, have it draw up later. First step towards self-loading crossbows. Grabbing hooks is another one. Pull into an open position, when something hits the trigger the "fingers" release and wrap around whatever it hits.

[krugaan]

There should really be a gnomish engineer, an eldritch knight refluff that, instead of casting spells, builds inventions which mimic wizard spells, and have the same limitations on uses per day. Just instead of preparing spells, the engineer refills tanks, calibrates gyros, or whatever. These inventions are so homebrew and complex only he can use them.

[zylodrizzt]

Parachute
As a reaction when you fall you may pull a cord to activate this item. This mimics feather fall except you only drop 10ft per round and have no control of where you land. Roll 1d8 every round you fall giving a direction for each number 1-8 1 south 2 sw 3 west 4 nw 5 north 6 ne 7 east 8 se you drift 15 ft in that direction. If you land and don't take off this item you move as if in difficult terrain. You may repack the chute on a short rest

[AugustNights]

I love this kind of stuff! I've written up some complex Tinkery Device rules for my own games, but let me see what sort of contraptions I have that fit this sort of thing. Enjoy or Critique!

Antichromatic Lens
A special lens for a bulls-eye lantern that reveals Anitchromatic Wax.
This dimly opalescent glass lens with a convex surface that can be easily fit onto a bulls-eye lantern. When light is cast through it, it causes Anitchromatic Wax to glow shimmer with a brilliant green hue that easily seen and reflects the light as brightly as a candle glows.

Anitchromatic Wax
A special wax that that only reveals with an anticrhomatic lens
This dim grey lump of wax, that spreads quite transparently on parchment, stone, or other materials that wax readily adheres to. Antichromatic wax is fantastic in that it doesn’t leave a visible trace (though it can be felt with a successful Intelligence (Investigation) check at Disadvantage). It can only be seen through a Antichromatic Lens.

Camera Mechanica
A peculiar little lens-box that captures the images on parchment.
Through a strange combination of metal plates and the physical oddities of light, this device has been constructed as a means to can physically capture the appearance of an image on parchment. With ten minute’s work and rigid stability requiring Concentration and no movement, a Camera Mechanica can create a gray-scale image of a still scene, object, or creature holding still. The image it produces is made on bit of parchment no larger than a human-hand in width and length. The image is easily ruined with oils of any sort, and thus should be well protected. The quality of the image is equal to that the creator making an Intelligence (Artisan Tools: Painting) Check equal to 10 + The Creator's Proficiency Bonus + Intelligence Modifier.

Clockwork Toy (Improved)
A windup toy that wanders across making a great din that can explode.
Clockwork toys come in many different appearances and often look like a tiny creature, humanoid, though more fantastical shapes can be found or made. These devices are designed to make a mechanical tin-like noise that replicates any sound within a volume range between a whisper and a human shrieking. When released, the clockwork toy wanders around on the ground, moving in random directions at a waking speed of 10 ft, and repeatedly making it’s tinny mechanical noise. It requires a Wisdom (Perception) check with Advantage to note that the noise is artificial.
If desired, the clockwork toy can be made with a particularly nasty self-destruct sequence, designed to activate when coming in entering into the same space as another creature. Such a clockwork toy bursts into shrapnel that deals 1d4 Slashing damage to the creature it has come in contact with. A Dexterity save reduces this damage by half.


Extension Gauntlet
An intricate gauntlet that can be extended and manipulated like a hand.
This clever tool is designed to allow a character to manipulate objects at a distance of 15 ft, and are occasionally favored by thieves who wish to pick locks or disarm traps at a safe distance. Though they can get a bit spendy if they are constantly being damaged by the traps they fail to disarm. All ability checks made to manipulate objects with the Extension Guantlet are made at Disadvantage. The extension gauntlet also functions as a Simple Melee Weapon that deals 1d4 Bludgeoning damage and has the Finesse and Reach properties.


Gonne
A hand-held device with a short barrel that launches round bullets by flintlock mechanism.
This hand-held device incorporates a smooth barrel that launches round bullets by the action of an explosive force, ignited by a flintlock mechanism. The gonne functions as a Martial Projectile Weapon that deals 1d8 piercing damage, and has a range of (60 ft/ 120 ft), with the Loading property.

Gum-rubber
An extremely bouncy compound popular for trap checking
This bouncy alchemical compound can often be found shaped into a ball the size of a human fist. When thrown with the same range as a Grenade Weapon it bounces directly away from it’s thrower traveling half the distance it was first thrown. It then lands and bounces again, covering half the distance of the previous bounce. The ball continues in this manner until it makes a bounce that would be less than 1 foot in length, at which time it stops bouncing and begins rolling. If the ball strikes a solid object, it reverses direction and continues bouncing or rolling. The savvy dungeon delver may use these gum-rubber balls to estimate how long a dark corridor is or to listen for odd sounds (such as a splash or a hallow sounding bounce). Gum-rubber bounces with a curiously soft force that seems to carry more weight that it could have. A gum-rubber ball can spring traps while bouncing, it springs any trap that will activate with (40 + Twice the thrower’s Strength score) pounds worth of pressure.

Kinetic Torch
A light producing device that doesn’t rely on fire, fuel, or magic.
This clockwork machination can be manipulated into the form of any lantern or torch. Changing the Kintetic Torch’s configuration requires an Action and both hands. Regardless of its form, A small crank extends from the kinetic torch, which can be turned as if by manipulating an object. Each turn the crank is operated, the Kinetic Torch produces light as a lit lantern of the type it is configured into until the beginning of its operator’s next turn. If the crank isn’t operated after that, the kinetic torch only produces dim light out to where the bright light would normally go for 1d4+1 rounds. Holding a Kinetic Torch only requires one hand, but operating its crank requires two. The kinetic torch requires no fuel to remain lit.

Puzzle Chest
An ornate wooden or metal puzzle that reveals a fist sized compartment when solved.
This curious puzzle contraption is difficult to understand at best. A Wisdom (Perception) check immediately reveals that the odd structure contains a hidden and complexly locked compartment, capable of hiding a fistful’s worth of goods. Ten minutes of close examination and a successful Intelligence (Investigation) check reveals the same information. Puzzle chests tend to be incredibly tricky to open through destruction or Strength and have their Burst DC increased by 5. While bursting the box will open the device, it does not open when damaged or destroyed due to hit point damage. A damaged puzzle chest simply won’t open until repaired. Any creature trying to open the puzzle chest can do so with ten minutes work and a successful Intelligence (Artisan Tool: Tinker) check, though the crafter of the device can always open it with an Action and no check.

Snapjaw Quick-Trap
A simple corded device that trips up anyone getting too close.
This cruel jagged device is designed to ensnare opponents and discourage them from stepping out of line. This device can be thrown as a Grenade Weapon, activating in whatever square it lands in. This device won’t deal any damage to any targets it directly hits, and instead lands in an adjacent unoccupied square as if the attack had missed. Any creature entering into this square must make a Dexterity Saving throw or suffer 2d4 Piercing Damage, flying creatures gain Advantage on this save. If the creature fails their saving throw, their movement speed is halved until they spend an Action to remove the device. Resetting this device requires little more than an object manipulation.
If a character spends an Action, they can hammer a Snap Trap into the ground causing it to effectively Grapple any opponents who fail their save against it.

Telltale Metascope
A peculiar mobile-like gathering of diverse measuring gyroscopes.
The telltale metascope serves a series of interesting functions. Depending on how it is spun, the telltale metascope can measure an incredibly diverse amount of data. By giving the telltale metascope a precises spin as an Action, its creator can determine any one of the following measurements: acceleration of a visible object; angle of two intersecting lines or visible objects in degrees or radians; arithmetic calculations of up to four digits; blood pressure and heart rate of a creature spun upon; color scale of object spun upon; crystal structure of an object spun upon; density of object spun on; direction towards center of plane of existence (aka “True Down”); distance in area or length of a visible object; fermentation efficiency of yeast or other fungi; force, torque, and power of an object spun upon; height in relationship to sea-level; local surface gravity; local atmospheric pressure; local force of seismic activity; local force of electromagnetism; local humidity; local temperature; ph balance of a liquid (enough acid will destroy the metascope); pitch and volume of local sounds; ratio of a visible curve’s circumference to its diameter (in relationship to pi); relationship to horizontally level; relationship to vertically plumb; relative age of object spun upon; spectrum of local light; status of local magic-fields (standard, wild, or null); sugar levels of a fluid; up to 30 minutes of time passing (measured in seconds or minutes); velocity of a visible object; and viscosity of a fluid.
Alternatively the telltale metascope may provide hours of entertainment as a odd top.

Wheely Boots
Hard leather boots with iron reinforcements and ball-barrings attached to the soles.
These strange boots provide incredible ankle support, and have large multidirectional ball-barrings attached to the soles. A character wearing wheely boots gains a +10 ft bonus to their walking speed but have their walk speed reduced by -10 ft when going up hill. When going down hill, a character moves an additional (5 x 1d4+1) feet in addition to every move they make. A character wearing wheely boots has Disadvantage on all Strength checks made to move or resist being moved, but gains Advantage when making a Shove check after moving at least 2 paces before doing so.

[krugaan]

Go go Gadget Helicopter! - fly 30'

Go go Gadget Hand! - mage hand

Go go Gadget Skate! - Expeditious Retreat