To achieve the combination of magic spell and creature, MtG combined two previously distinct features, the Enchantment Creature typeline and the Saga enchantment type, making cards that both possess combat power and advance magical effects before the creature is sacrificed
On every Rayquaza card, they've succeeded with aplomb at their assigned task of drawing an angry dragon
Youre left with a powerful Incubator token that gives you board presence, plus it has synergies with token and artifact-matter cards
With access to 4 colors, there are an absolute ton of ways to get multiple lands onto the battlefield each turn, sometimes even at instant speed, meaning something as innocent as a Harrow can suddenly turn into 4 life and a combat trick or two
You can use it for its intended purpose of copying a spell, or run it alongside free spells like Fury and Force of Will to guarantee you have the right card to pitch every game