For your First Game of Sentinels of the Multiverse, we recommend playing against Baron Blade. He shows off what Villains can do without being immediately overwhelming.
When playing against Baron Blade for the first time, DO NOT shuffle his deck! The top card of the deck is the "Mobile Defense Platform", which you'll need for his setup. The rest of the deck is in an order that provides a good first game experience, so just put it into the play area without shuffling, and you're good to go! This order of cards is also listed in the Lore Book.