When a card or effect is activated that would destroy a card on the field (Quick Effect): You can banish 1 Zombie monster from your GY
Blue and green can potentially untap him several times in a single turn, and all three colors offer enough proliferate and counter-doubling to potentially ultimate a planeswalker when you first summon it (and thats without a Doubling Season)
its airbending trigger also removes threats, albeit temporarily, or you can use it to pseudo-flicker your permanents
A white-blue-black that costs four total mana, hes a 3/3 with incredible abilities for being that mana-cheap, including First Strike, vigilance, AND menace
A 1st Edition Venusaur PSA 10 runs from about $5,000 into the tens of thousands , and 1st Edition Blastoise reaches similar highs, a top Gem Mint copy has sold near $88,000