As a Commander or part of any deck, Yuna, Hope of Spira works really well with all kinds of enchantments and some kind of mill/discard strategy that lets you get those expensive enchantment creatures into your graveyard so you can then cast them for free
And of course, you can still attack and block with it
This one looks like Byoog
With modern design sensibilities, I think we could get something far better than what we have to work with right now
You only get to do this two times, then it defaults to a generic 6/5 creature with trample, but you're either going to get two free spells, or you're putting pressure on your opponents to remove a potentially game-ending problem
Serrated Scorpion is a 1-black 1/2 that deals two damage to each opponent and gives the controller two life, and Whisper Squad is a 1-black 1/1 that can bring out more of itself for two mana