Players can represent Gunk cards using objects from outside the game so long as the game state remains clear and understandable to all players
Which is what you need
To determine their rarity, you must look them up on an online database like Scryfall or Gatherer
I find the other anon's comment weird though (I was the one who made the first reply)
They are: Aeve, Progenitor Ooze Experiment Kraj Felix Five-Boots Mimeoplasm, Revered One Prime Speaker Vannifar Slogurk, the Overslime Slurrk, All-Ingesting The Mimeoplasm Umori, the Collector Vannifar, Evolved Enigma Aside from them, there are other commanders that synergize with oozes and their abilities, including: Atraxa, Praetors' Voice: Proliferate Muldrotha, the Gravetide: Reanimation Adrix and Nev, Twincasters: Token doubling Xavier Sal, Infested Captain: Proliferate and populate Morophon, the Boundless: 5-color shapeshifter commander Yidris, Maelstrom Wielder: Cascade Shalai and Hallar: +1/+1 counters Wrap Up Biogenic Ooze | Illustration by Lake Hurwitz Woof