A bird trying to steal trinkets; how to handle it mechanically?

[King of Nowhere]

I have this idea for an unconventional monster: a magically mutated magpie that can recognize magic items and will selectively steal them. eating magic items will grant the bird some magical powers. the players will be raided by such birds trying to steal rings or amulets.

the problem is, how do i make a check for it? the rules only contemplate two ways to take away objects worn by another creature: by a sleight of hand check (which the magpie, having 1 hit dice, would be unable to perform effectively; furthermore, i'm not even sure there are provisions for trying that during a battle) and a series of grapple check which, with size penalties, aren't worth considering.
i would like the magpie to have a decent shot at stealing stuff. if evolution rewarded it, then the chance of getting killed must be lower than the advantage granted by the extra powers. on the other hand, i don't want it to be an automatic success, and i would like it to be some kind of opposed roll. how can i achieve it?

[SangoProduction]

Pathfinder has the steal maneuver. Of course, that explicitly cannot work against things that are closely worn (like rings). And fastened items like amulets and capes would cause a -5 to the check.
As you did not mention that, I am assuming this is 3.5. Which also has a ruling against worn items against rings. So similarly does not work. But hilariously, if you can beat a DC 40, you can lift every single not securely worn item as a couple free actions.

You are saying you want a mutant. There's no reason to stick with the standard magpie stat sheet.
Of course, no raw rules, outside of perhaps spells, allow you to simply do that. So changing stats doesn't matter for your purposes.

Now, Heat Metal spell...that'll get the bloody jewelry off people real quick.

[Venger]

I have this idea for an unconventional monster: a magically mutated magpie that can recognize magic items and will selectively steal them. eating magic items will grant the bird some magical powers. the players will be raided by such birds trying to steal rings or amulets.

the problem is, how do i make a check for it? the rules only contemplate two ways to take away objects worn by another creature: by a sleight of hand check (which the magpie, having 1 hit dice, would be unable to perform effectively; furthermore, i'm not even sure there are provisions for trying that during a battle) and a series of grapple check which, with size penalties, aren't worth considering.
i would like the magpie to have a decent shot at stealing stuff. if evolution rewarded it, then the chance of getting killed must be lower than the advantage granted by the extra powers. on the other hand, i don't want it to be an automatic success, and i would like it to be some kind of opposed roll. how can i achieve it?

Advance it so it has more hd and its sleight of hand is better. If that's not enough, give it an arbitrary racial bonus. If that's not enough use one of its feats for shape soulmeld (theft gloves) and another for master pickpocket. You're absolutely allowed to make soh checks during a battle and with something someone is wearing or holding, you just take a penalty. Grappling does not do anything regarding stealing stuff You may also consider refluffing the ethereal filcher or ethereal marauder who are magpies for magic items. When someone tries to use soh against you you are entitled to a spot check to notice, so that ought to be enough for at least one of your pcs.

[Palanan]

Originally Posted by King of Nowhere
I have this idea for an unconventional monster: a magically mutated magpie that can recognize magic items and will selectively steal them. eating magic items will grant the bird some magical powers. the players will be raided by such birds trying to steal rings or amulets.

This is very close to Pathfinder’s witchcrow (https://www.d20pfsrd.com/bestiary/monster-listings/magical-beasts/witchcrow/), and as Sango noted you can use the Steal mechanic.

[Toliudar]

This creature is crying out to have Flyby Attack as a bonus feat.

And +1 to everything Wenger said.

[King of Nowhere]

problem with the steal mechanics is that it uses the combat manuever modifier, which uses str and size bonus. a bird would have no chance.
a racial bonus to sleight of hand would seem the best choice

[Doctor Awkward]

I will second the racial bonus to Sleight of Hand checks.
Perhaps a racial ability that allows it to add it's size bonus on Hide to SoH?

In real life magpies are exceedingly intelligent birds so an Intelligence high enough for multiple skill points might suit fantasy.

[Thurbane]

The Spellgaunt from MM2 has similar behaviours, and uses a disarm attempt to snatch items.

[daremetoidareyo]

Huitzel from races of dragon magic fits the bill. Use sleight of hand checks to see if they got it. If they're not being sneaky, players will figure out why that leathery bird just hit them

[denthor]

Look at a filturer? Spelling. 3.5 edition adaptation for what you need.

As far as the bird Idea deeper slumber spell by the mage of which the bird is the familiar, allows opportunity so to get rings and cloaks. Illusion of several birds or even summoned birds that look alike cause players not to know which is real.

Complicated messy and possibly two caster needed to pull it off.