The hammer throw bonus is a very tricky one to get, and it took me numerous tries. Heres how i did it: To throw the hammer, you have to be in the air, not swining the hammer, while falling down. I sugust you go to the Brinstar level, jump into the acid, and get your character in that position. When your character is falling, right before s/he starts swinging again, press Z+Smash the control stick(in any direction), and your character should throw the hammer in the direction of the control stick. Note that if you fall in the acid and drop the hammer, that won't count as the acid made you drop the hammer, not you yourself. Also, you will need super precise timing to pull the throw off. I did it with Mario. I got myself launched into the air, and franticly smashed the control stick in any direction while pressing Z like a madman.