Its power and toughness grow with every card in your opponents graveyards, and every spell you cast feeds it more
Lifegain is a popular theme in Commander games, and this does what you want, giving you the lifegain trigger or a card
Use the creature's power as it last existed on the battlefield to determine how much damage it deals to the target
Since you aren't casting Themberchaud, the commander tax doesn't increase, even if he dies
Rather than getting rid of absolutely everything, Wakening Suns Avatar only destroys non-dinosaur creatures
While Wizards learned long ago that fast mana is problematic, it still likes to mess around with cost-reduction effects for some reason, which leads to 13/13, flying, trampling Mindslavers that cost only six mana