1) Some larger skeletal monster that has smaller skeletons inside. The smaller ones do break to bits but they are indestructible. Careful team management of the lowly monsters lets you focus on the main monster. Maybe the main one can be rooted to the spot or it moves very slowly and it uses its minions to distract and occupy the players. The Larger Skeletons from Castlevania 64 could be one idea and make them humanoid, or just have some skeletal creature like a porcupine or something similar.
2) In Ray Harryhausen style, some kind of Troglodyte monster would be ideal. To mix it up a bit, make the encounter be based around two of them with different attacks and supportive abilities. That might be a caster type and a warrior type, so the team would need to figure out which one they need to focus around first. Would also look awesome with stop-motion animation.
3) Centaur. Classic mythical beast which could be an interesting battle. Attacking its legs to make it drop and then being able to attack it. Centaur's are classical bow and arrow uses, so having a more ranged focused enemy, replete with traps for the team etc could make for an interesting battle that would require a bit more thought and not just straight hack and slash.
4) The Hydra. Also a classic monster. Fairly slow moving but the multiple heads are always going to cause issues for many. You could make it a mobile version and have it slowly moving around, or you could have it locked in a static place in water and use the heads to mix in close combat and some ranged attacks.
It really depends if Brazen is going to stick to the classic Harryhausen style monsters, or if they will open it up to some other creatures that are done in the same style. Maybe taking cues from Japanese mythology