how did garfeild(beastboy) get his powers in the first place

Hi savedanny! Well, we neva get told in the animated series, but in the comic libros (so i'm told) this is how BB gets his powers:
BB is terminally ill and is going to die, so his father (who is either a scientist o a doctor I can't remmeber) as a last resort does a procedure to try and save his life. The procedure works but also turn BB green. Later on though, BB is bitten por a monkey (aparently the monkey was green too!) and his DNA mixed with the animal DNA easily because the procedure made his DNA unstable. This gave him the power to change into animals!
Hope this helped!!! :-)