Do you mean that the troll boss's sprite changes when he attacks
No, there is a troll boss that attacks like the one from lvl 1 but is stronger. that one is fine. The issue is that another troll has the attack from the plant and by this I mean that it attacks very slow but deals a lot of dammage. Attack animations are the troll ones, but if you loose the s*x animation that plays is the plant one. I assume the plant boss on lvl 4 uses the troll sprite and attack animations, but has the correct attack pattern and s*x animation
Just checked and is still there. I'll try to explain it as clear as possible: let's say that an enemy has 1) sprite; 2) attack animation; 3) attack pattern (speed and damage the enemy does); and 4) s*x animation.
On lvl 4 all anemies from all previous levels appear, even bosses. It's here where the problem is. The level 3 boss (the plant looking one) uses the sprite and attack animation from the level 1 boss (the troll with a stick) but the attack pattern and s*x animation are from the level 3 boss.
Note: now I'm too strong to lose so I can't check the s*x animation that plays there, so maybe now it uses the one from the troll as well.