Koma, Cosmos Serpent

Mana cost: {3}{G}{G}{U}{U}
Type: Legendary Creature — Serpent
Power / toughness: 6 / 6
Set: Kaldheim #326 (mythic)
Price: $6.50 USD

This spell can't be countered.
At the beginning of each upkeep, create a 3/3 blue Serpent creature token named Koma's Coil.
Sacrifice another Serpent: Choose one —
• Tap target permanent. Its activated abilities can't be activated this turn.
• Koma gains indestructible until end of turn.

Koma, Cosmos Serpent has 8 printings, first in Kaldheim (2021). EDHREC ranks it #1,470 among Commander cards. It appears most in Kiora, Sovereign of the Deep decks (6,227 on EDHREC). 1 public deck on TCG runs it. It has 5 official rulings.

Legality

commander: legal
legacy: legal
vintage: legal
pauper: not legal
modern: legal
pioneer: legal
standard: not legal
brawl: legal

Public decks that run Koma, Cosmos Serpent

Deep Clue Sea - Murders at Karlov Manor Commander, led by Morska, Undersea Sleuth

Commanders that run Koma, Cosmos Serpent most

Deck counts from EDHREC.

Kiora, Sovereign of the Deep: 6,227 decks
Aesi, Tyrant of Gyre Strait: 5,616 decks
Helga, Skittish Seer: 5,471 decks
Kenessos, Priest of Thassa: 5,125 decks
Zimone, Mystery Unraveler: 5,081 decks
Kinnan, Bonder Prodigy: 4,610 decks
Adrix and Nev, Twincasters: 4,153 decks
Galadriel, Light of Valinor: 4,134 decks

Often played with Koma, Cosmos Serpent

Cards that show up in the same decks on EDHREC.

Rulings

2021-02-05: A spell or ability that counters spells can still target Koma, Cosmos Serpent. When that spell or ability resolves, Koma won't be countered, but any additional effects of the countering spell or ability will still happen.
2021-02-05: The first mode of Koma's activated ability doesn't stop static abilities from affecting the game, and it doesn't stop triggered abilities from triggering. Unlike similar effects, it does stop mana abilities from being activated. Most activated abilities that produce mana as they resolve are mana abilities.
2021-02-05: If you choose the first mode of Koma's activated ability, you can choose a permanent that's already tapped as the target. The effect stopping its activated abilities will still apply.
2021-02-05: You can't sacrifice Koma itself to activate its last ability, but you can sacrifice any other Serpent you control, including Koma's Coil.
2021-02-05: Activated abilities contain a colon and appear in the form "[Cost]: [Effect]." Some keywords such as equip are activated abilities and will have colons in their reminder texts. Loyalty abilities of planeswalkers are also activated abilities.