Hey, first post and all.
Anyway, I found the shield to be pretty useful against some bosses. In fact, when fighting Mother Nature, I didn't know that she is vulnerable to energy form shots, and tried to use the shield to bounce off her fireballs back at her until I became frustrated and came here, and found out how to kill her.
I found out about the form-changing-with-keys thing, but was so used to using the mouse to do it that I decided to finish the game that way.
One of my favorite strategies (might've been mentioned before) is against the Creator's first form, which essentially makes him the quickest boss in the game. Basically, if you can set a well-placed thorn up behind his head, it kills him in one hit. (if you can get it in the right spot)