What are his best talents
I've been a long time user of Skull Mage. My recommendation might be a bit oudated though:
Art of War.
Skull mage hugely relies on mercs when he's on his own. When paired with other wizard heroes though, like Ambrosia and Pan Goli, I would hypothese that going for Fatal Strike would be more usable for Skull Mage in modes other than Battle Royale. Fact is that he attacks very rapidly. So getting a lot of crits will surely yield a lot of dmg. Especially when paired with Toxic Shaman main and Djinni hero aid.
I also run a wizard br team and I currently run shining wizard,pg and Demon slayer as aids for more mercs. Other then Bullhead what other 2 heroes should I use as aids for my wiz team?