First, the ability to exile opposing creatures or your own is a versatile effect, and upon ETB means it's something white is well equipped to repeat
Each of them revolves around a specific Pokemon: Charizard, Mewtwo, and Pikachu
Bulwark Ox Bulwark Ox looks incredibly impressive to me based on the success of Luminarch Aspirant
She reins over agriculture, irrigation, inspiration, and fertility
March of Swirling Mist is the weakest of these because its constrained by mana or cards, but the fact that the spell actually does something itself, answering things like Collector Ouphe or protecting your creatures, makes it good enough to play
Similarly, a [X] cost becomes "Reduce enchanted creature's toughness by X." You can't pay a cost that would reduce enchanted creature's toughness to less than 0