Five decks tied to Ikoria: mutate, cycling, keyword counters, Human tribal and an Izzet spell copying deck.
Cast a mutate creature over or under a non-Human creature you control and the two become one permanent with the top card characteristics and all abilities from the stack. Every mutation triggers the mutate abilities again, which is where the value comes from.
Pay a cost, discard the card, draw a new one. Ikoria built a whole deck around getting paid for it, so cycling here is a trigger rather than a consolation prize.
Ikoria introduced counters that grant keywords, like flying or deathtouch, rather than stats. The Abzan deck pulls those keywords out of the graveyard and staples them onto one creature.
Companion lets a card start outside the game if your deck meets its restriction. In Commander it acts as a ninth card in the opening hand, which is why the mechanic was quickly reined in.
Commander 2020 arrived with Ikoria and is one of the more mechanically adventurous batches. Mutate is the headline, and it is still the strangest of the bunch: your creature becomes a stack of cards that keeps triggering every time you add another.
Cycling is the other standout. Timeless Wisdom made cycling a payoff engine instead of a way to smooth draws, and Gavi remains a reasonable budget commander for that plan.
Every deck in the batch also came with a companion card, which was the format's introduction to a mechanic that got errata'd within months. The decks still function fine without leaning on it.
Timeless Wisdom is the cheapest deck to make good, since cycling payoffs are inexpensive. Enhanced Evolution is the one worth playing if you want a mechanic nobody at the table remembers how to resolve.
Kalamax, the Stormsire
A Temur spellslinger deck from Ikoria built to copy instants. Kalamax, the Stormsire copies your first instant each turn while tapped and grows every time, so the deck attacks, holds up mana, and doubles its spells for token armies and burn.
Otrimi, the Ever-Playful
A Sultai mutate deck led by Otrimi, the Ever-Playful, stack mutate abilities on a single creature to build an unstoppable monster, and when it dies, Otrimi brings it back to your hand to do it all over again.
Jirina Kudro
A Mardu humans tribal deck led by Jirina Kudro, create Human soldier tokens scaled to how many times you've cast Jirina, give all your Humans +2/+0, and overrun opponents with a wide aggressive army.
Kathril, Aspect Warper
An Abzan graveyard keywords deck led by Kathril, Aspect Warper, fill your graveyard with creatures carrying powerful keywords, then cast Kathril to distribute those keywords across your entire board and attack with an unstoppable army.
Gavi, Nest Warden
A Jeskai cycling deck led by Gavi, Nest Warden, cycle cards for free every turn, generate 2/2 Dinosaur Cat tokens on your second draw each turn, and trigger cycling payoffs that punish opponents with damage and counter effects.