Hehe I like it.
That you can be hurt when jumping on an enemy can be annoying though. Do you have an event that is comparing the ground detector Y of the player to enemy.top so to speak.
Ground detector does not overlap solid (which means the player is jumping/falling)
+Player hitbox overlaps enemy hitbox
+Ground detector Y greater (below) enemy hitbox.Y + 8 (for example, +8 being a tolerance)
=> hurt player
Ground detector does not overlap solid (which means the player is jumping/falling)
+Player hitbox overlaps enemy hitbox
+Ground detector Y lower or equal (above) enemy hitbox.Y + 8
=> kill enemy
Or at least something like that. All assuming you have a ground detector and hitboxes and stuff.
And I guess I found a bug: when I was jumping into the water above, Buttweasel disappeared
<img src="http://img237.imageshack.us/img237/6757/buttw0ul0.png">