These promotional cards have a high chance of being rather expensive collectibles
That leaves us with a lot of ground to cover, but it also means that, for mythics especially, the presence of a mythic from a specific set likely means that it will be the only one, due to overall space constraints

Gallery and List of Godzilla MTG Cards Anguirus, Armored Killer (Gemrazer) Babygodzilla, Ruin Reborn (Pollywog Symbiote) Battra, Dark Destroyer (Dirge Bat) Bio-Quartz Spacegodzilla (Brokkos, Apex of Forever) Biollante, Plant Beast Form (Nethroi, Apex of Death) Destoroyah, Perfect Lifeform (Everquill Phoenix) Dorat, the Perfect Pet (Sprite Dragon) Ghidorah, King of the Cosmos (Illuna, Apex of Wishes) Gigan, Cyberclaw Terror (Gyruda, Doom of Depths) Godzilla Plains Godzilla Island Godzilla Swamp Godzilla Mountain Godzilla Forest Godzilla, Doom Inevitable (Yidaro, Wandering Monster) Godzilla, King of the Monsters (Zilortha, Strength Incarnate) Godzilla, Primeval Champion (Titanoth Rex) King Caesar, Ancient Guardian (Huntmaster Liger) King Caesar, Awoken Titan (Snapdax, Apex of the Hunt) Mechagodzilla, the Weapon (Crystalline Giant) Mothra, Supersonic Queen (Luminous Broodmoth) Mothras Great Cocoon (Mysterious Egg) Rodan, Titan of Winged Fury (Vadrok, Apex of Thunder) Spacegodzilla, Void Invader (Void Beckoner) What Formats Are They Legal In

One is the obvious scarecrow tribal, and the other is shapeshifter tribal with changeling
So far, we only know of three cards, Demonic Tutor, Opt, and Swords to Plowshares, so it seems like Opt at least will still be playable in Historic when the cards release next month, as befits a card already legal in standard