Multiplayer mode- When opening up ammo boxes, 4 mini ammo boxes spawn- 2 for each player. if one player opens an ammo box while the other player is far away, the 2 remaining mini ammo boxes begin bouncing off of the walls attempting to get to the other player.
Multiplayer- if players enter different portals, game refuses to continue.
Unknown if bug or intended behavior (no screenshot)- Cursed crystal caves boss will spawn in walls (no-clipping without destroying any walls) and circle players before actually spawning