I've written an article that covers tournament legality as much as is currently possible if you'd like to learn more
Mana Curve The mana curve shows there are plenty 2-3 drops
The former simply doubles the mana generation of your basics when casting X spells (at the cost of colorless mana), letting you punch way above your usual station in a game
While you might think that being forced to play only Humans would be a significant downside, it turns out there are so many cheap, powerful Humans in the game that Humans was a tier-one Modern deck for a couple of years prior to Modern Horizons
It only costs one mana as well, making it easy to build up counters early in the game
(You and planeswalkers you control can't be targeted, dealt damage, or enchanted by anything controlled by that player.) When this creature enters, if you cast it, target opponent takes an extra turn after this one