There's 2 strategies:
1. attempt to reach it without a full stomach (difficult)
2. reach it with a full stomach and punch it to death
the final boss actually isn't too strong. It's the common enemies that are the problem. Try to funnel them all through the hole in the room, hiding behind the wall to get sneak attacks. Never let a cake catch you. They're slow, but they stun you for 5 turns on attack. If a cake attack is unavoidable, eat the cake first.