Please recommend a couple of monsters

[gfishfunk]

I have 4 adventurers, all level 3 (Melee Druid, Warlock, Sorcerer, Bard).

They are fighting their way to the top of a small tower, 30' up from the ground outside. fighting humanoids (already with stats). At the top, they will fight a low-level caster and a Spectator (mini-beholder from monster manual). A third party is going to sweep in, do some exposition and dialogue, and then call on a monster - some kind of abomination - to come in from the forest to fight them.

I am looking for a very tall monster for the party to fight as a 'boss battle' appropriate for their level (which I do not think 5e does really well). I would like the monster to be around 40' tall. Thematically, an abomination-type monster would work, but a fiend would also do.

Can anyone make a suggestion? I'm away from book right now and planned to work on this last night, but I ended up with no time.

[Gastronomie]

Due to the fact that no matter how strong a monster may be, it can take only one action in a single round (unless it's Legendary), boss monsters are overall a bad idea in this game.

How about making it so large that each body part can be treated as a different monster (using stats of a particular monster for each body part, each with its own initiative)? For instance:

Head: Copper Dragon Wyrmling (CR 1, 200XP, Bite and Acid Breath, fly ability can be re-fluffed into the simple fact that the giant monster's head is pretty far up)
Arms: Giant Octopus x2 (CR 1, 200 XP, Grapple can be like a grasping giant hand)
Legs: Giant Goat x2 (CR 1/2, 100XP, Charge ability can be like a "kick")

Now, add their XP together: 200+400+200=800
Then multiply it by 2, based on DMG page 82's "Encounter Difficulty" determination instructions to get 1600.
Divide this by 4 for 400, take a look at the table... and you'll see that this encounter is "Deadly" for four Level 3 adventurers.

So you might want to tweak up the above a bit more. Perhaps change arms to non-giant, normal "Constrictor Snake"s or something else.

But anyhow, get what I mean? I think this is much better than simply having a CR 5 monster or something like that fight the adventurers (it's risky and can get people killed too easily, depending on just the initiative roll).

[RickAllison]

Here goes! Note that you can scale any creature up to Huge or Gargantuan size and they will do for what you would like. The only change that needs to be made (and you would need to recalculate CR) is changing the multiplier of the damage dice and give it d12 or d20 hit dice instead of its regular.

Giants. Huge (so they are big enough that you can just scale them up without worrying about damage or HP), varied, and they usually have a variety of attacks.

Hydra. Huge again, a monstrosity, and rather easy to adjust for damage. If you feel like it is being too lethal (CR 8 and all), have it attack with fewer heads, or have some heads competing for food.

Remorhaz. Huge monstrosity. Probably too dangerous, however.

Barlgura. Large fiend, but this one might not need to be scaled up... CR 5, it can high jump 20 ft (so it can easily reach the party), and it has a climb speed (so it can move about the tower to ambush and make it seem more boss-like. Invisibility means it can present an unseen threat until the attack starts.

Bearded Devil. Scale it up (more HP, mainly) and this would be good.

Displacer Beast. This might seem weird, but give one of these a climb speed and this could be powerful.

Gorgon. Scale it up to Huge, have it try and bring down the tower itself.

[gfishfunk]

That is a great idea. Generally in 'boss fights' I create several minions to be doing something else for action economy and challenge, but that did not fit this cinematic battle.

Your idea is very good.

I think I might do three parts rather than five: the head, and two arms. I might up the CR on the head and add hitpoints, lower the HP on the arms....I'll chew on it.

[JeffreyGator]

Zombify a T-Rex, CR 8 but perhaps reduced since they see it coming as a zombie and it is slower.

Abberations:

Huge Chuul (CR 4 + Huge)

Huge Otyugh (cr 5 + Huge)

Multiple Giant constrictor snakes that slither up the tower...

[gfishfunk]

So, I built a creature a few minutes before the game as a giant centipede with large crab-like claws. The head was an enemy, the arms were an enemy, and the tail was an enemy. They, of course, focused all attention on the head. Once the head died, the limbs kept moving, which annoyed my players, but they rolled with it. It was a good boss-fight.

[FightStyles]

So, I built a creature a few minutes before the game as a giant centipede with large crab-like claws. The head was an enemy, the arms were an enemy, and the tail was an enemy. They, of course, focused all attention on the head. Once the head died, the limbs kept moving, which annoyed my players, but they rolled with it. It was a good boss-fight.

You should have made the head invulnerable to damage until one of the limbs was destroyed. Kinda Zelda-esque type of boss fight. They might not have been as annoyed with that.

[Estrillian]

You can always give a lower level monster a legendary action as well (probably 1 per turn) to up the action count a little. I've given boss monster a legendary action with a recharge, so that it is clearly a special attack.

For your situation how about some sort of huge corrupted treant? A Tree Blight like the one appearing in the back of Curse of Strahd would fit the bill. It gets a multiattack that allows it to grapple with its roots multiple times, as well as smashing with its branches (you might want to allow grapples with the branches too) and can use a bonus attack to bite a grappled thing. Give that a legendary action as well and you have a good 3-5 actions a turn.

Not enough monster have good reactions though, might want to add one of them.

[gfishfunk]

Not enough monster have good reactions though, might want to add one of them.

Very true.

This encounter has come and gone, however. My players enjoyed it, I think.

[supergoji18]

Have a Goristro knock down the tower, then have the players fight it.

Make sure you grab your popcorn as you watch this thing horrifyingly eviscerate everything there.

... or just use a giant.

[PoeticDwarf]

Due to the fact that no matter how strong a monster may be, it can take only one action in a single round (unless it's Legendary), boss monsters are overall a bad idea in this game.

How about making it so large that each body part can be treated as a different monster (using stats of a particular monster for each body part, each with its own initiative)? For instance:

Head: Copper Dragon Wyrmling (CR 1, 200XP, Bite and Acid Breath, fly ability can be re-fluffed into the simple fact that the giant monster's head is pretty far up)
Arms: Giant Octopus x2 (CR 1, 200 XP, Grapple can be like a grasping giant hand)
Legs: Giant Goat x2 (CR 1/2, 100XP, Charge ability can be like a "kick")

Now, add their XP together: 200+400+200=800
Then multiply it by 2, based on DMG page 82's "Encounter Difficulty" determination instructions to get 1600.
Divide this by 4 for 400, take a look at the table... and you'll see that this encounter is "Deadly" for four Level 3 adventurers.

So you might want to tweak up the above a bit more. Perhaps change arms to non-giant, normal "Constrictor Snake"s or something else.

But anyhow, get what I mean? I think this is much better than simply having a CR 5 monster or something like that fight the adventurers (it's risky and can get people killed too easily, depending on just the initiative roll).

Nice idea you've got there

[Gastronomie]

Nice idea you've got thereThanks~.

Well, I suppose this sort of method could be altered to fit boss encounters at various levels (I actually wanna do it soon in a particular game I'm DM'ing).

Nice to hear it went well. :)

[Estrillian]

Very true.

This encounter has come and gone, however. My players enjoyed it, I think.

What did you decide to do in the end, if you don't mind me asking?

[tieren]

I was going to recommend an awakened tree, maybe sporting a couple of parasitic vine or needle blights.

[gfishfunk]

What did you decide to do in the end, if you don't mind me asking?

The creature had a claw, a head, and a tail, each separate creatures with separate stats and initiative slots.

The head had the most HP, and did a simple 2d6 damage on hit.

The claw did less damage, but could knock a person prone.

The tail did more damage, and forced a save for the poisoned condition.

Most of the stats were homebrewed, but based on things in the book that were all around 100 xp to 450 xp. Everything was simplified a bit to reduce the difficulty because they were coming off of what appeared to be a smaller fight but was, in fact, a higher damaging fight against an evil cleric and a Spectator.