The first spirit ball is found in the creature just after the 4 stone pillars but watch out for the zombies just before it.
If you are in two-player mode, let one of you collect all the spirit balls until you turn into the beast as that player can now protect the other player until he can turn into the beast.
Avoid the blue demons by jumping over them or onto a higher level. If Nelf himself appears to rise up and you are in one-player mode, rush into him to get the end of level baddy. Just hold the fire button down and face him for best results.
The main problems here are the jumping head-eaters. Kick or low-punch then when they're on the ground. The rattles of the snakes should be kicked to destroy the snake. The end-of-level baddy is no problem. Go underneath the dish spewing out eyeballs and put on the autofire.
The main problem on this level is the mass of running chickens. Stay in the middle of the screen near to the top if possible. When you become the beast, keep pressing fire to keep somersaulting long as there aren't any holes.
Only use your breath on the end-of-level baddy; keep pressing right and fire to breath on it. After it has moved in a bit, follow it and repeat the above procedure to kill it.
When you become the beast use ducking punches instead of the special weapon. When you come to the Nelf-created creature go to the far right-hand side of the screen and hold down fire.
Stay high up all the time on a slate in the middle of the screen as on level 3, otherwise the fish will turn into wheels and run over you about three times
When you get to the end-of-level monster just jump over him, hit him once, jump over him again, hit him again and repeat this until he's dead.
At this stage you need at least one full life if in one-player mode; anything less and you've got no chance. However in two-player mode it isn't much of a problem.