When Zygon Infiltrator becomes a copy of a creature, it's neither entering nor leaving the battlefield
Nevil itself for the jump, including your opponents creatures
That's not to say Garth is weak , but he's definitely fair: this card's schtick is that it's a powerful wizard that can cast iconic Alpha spells, and the card nails that flavor, letting you cast six of the most iconic spells from the original Magic set, with the biggest draw being the ability to cast a friggin' Black Lotus in Commander
SPACE OPERA DISCO INFERNO Cut Propulsion is really nice removal in mono-red, actually
Then, Avalanche, Grab Your Sword, and Tinker Bell Giant Fairy all do damage to multiple opponents, setting up those combos easier late game
Most white creature decks should at least consider this in the 99