kellan mtg card Joins Up (You may cast it as a sorcery on a later turn without paying its mana cost.) Whenever a legendary creature enters the battlefield under your control Kellan, the Kid - 24/54

Wan Shi Tong, Librarian is a good flash threat in a longer late game, but its also good early since it draws you a card and you can return it to your hand via ninjutsu

The rate here is absurd

Creatures with this ability function similarly, leveling up as the cost is paid, but require Experience Counters, allowing them to be manipulated by effects like Propagate, and replacing their power, toughness, and abilities as they level up

Planeswalkers are a good start, among other options

This gives the player an advantage in that their opponent is forced to either damage themselves or allow them to recast a potentially game-winning creature