Don't waste boosts on Doomwood. Just bot overnight and such. In a private room with a warrior, it took me about 24 hours to get Necromancer without any boosts. Botted the 24 hours straight. Easy. Just don't rush things.
Wow buddy, I dont think you should be trying to solo creature creation at level 21... I recommend you level up and kill him with friends/randoms. And also use a bot + rep boost over night for rank 10's