mtg card terms Magic: The Gathering Definitions: Community Jargon! Part 2 Magic: the Gathering Basic Definitions:

If you have any doubts, try to understand on which turn a card is good, how much mana or how many resources you need to optimize it, and how many similar cards you already run

This probably makes it overly useful in Standard or Limited, but its Commander potential is huge, and I can see why it's been included in the Avengers Assemble precon

When you click on that youll be given options on the right side of the screen, with legal decks available to play that option on the left side

There is no mention of a minimum or maximum mana cost for the creature , meaning you could theoretically bring any creature to the battlefield for free