Miirym, Sentinel Wyrm

Ceremorphosis — When this creature enters, turn any number of target tapped nontoken creatures face down. They're 2/2 Horror creatures.

Flash Flying When this creature enters during the declare attackers step, for each attacking creature, you may reselect which player or permanent that creature is attacking. (It can't attack its controller or their permanents.)

4, T: Roll a d20. Each opponent exiles cards from the top of their library until they exile an instant or sorcery card, then shuffles the rest into their library. You may cast up to X instant and/or sorcery spells from among cards exiled this way without paying their mana costs. 1—9 | X is one. 10—19 | X is two. 20 | X is three.

Flying Whenever a Dragon you control is dealt damage, it deals that much damage to any target that isn't a Dragon.

This land enters tapped unless you have two or more opponents. T: Add R or G.

When Volo enters, create Volo's Journal, a legendary colorless Book artifact token with hexproof and "Whenever you cast a creature spell, note one of its creature types that hasn't been noted for Volo's Journal." 2, T: Draw a card for each creature type noted for target permanent you control named Volo's Journal. Choose a Background

If you would put one or more counters on a creature or planeswalker you control or on yourself, put that many plus one of each of those kinds of counters on that permanent or player instead. Choose a Background (You can have a Background as a second commander.)

Myriad (Whenever this creature attacks, for each opponent other than defending player, you may create a token copy that's tapped and attacking that player or a planeswalker they control. Exile the tokens at end of combat.) Instant and sorcery spells you cast cost 1 less to cast. You may cast sorcery spells as though they had flash.