This helps to set up Asmoranomardicadaistinaculdacars surprisingly potent removal effect, which one can only imagine involves force-feeding opposing creatures to death, and can even bring her back later on if need be
But either way, once they reach their final form, they become big, often flying, creatures
You may either change those targets to be legal in reference to you, or, if those are the spell's only targets, the spell doesn't resolve for having illegal targets
Destroy all creatures with power 3/4 or greater
Arboria Bazaar of Wonders Caverns of Despair Chaosphere Concordant Crossroads Elkin Lair Eye of Singularity Field of Dreams Forsaken Wastes Gravity Sphere Hall of Gemstone In the Eye of Chaos Koskun Falls Land's Edge Living Plane Mystic Decree Nether Void Null Chamber Pillar Tombs of Aku Revelation Serra Aviary Storm World Teferi's Realm The Abyss Tombstone Stairwell Winter's Night