Coram, the Undertaker

Coram, the Undertaker gets +X/+0, where X is the greatest power among creature cards in all graveyards.
Whenever Coram attacks, each player mills a card.
During each of your turns, you may play a land and cast a spell from among cards in graveyards that were put there from libraries this turn.

Modern Horizons 3 Commander

Coram's first ability applies only while it is on the battlefield. In all other zones, its power is 0.

If it's your turn, you control Coram, and another player has permission to play a card in a graveyard that was put there from a library this turn (perhaps because it's an instant card they own that has flashback), whoever gets priority sooner will have the first chance to play that card. In most cases, this will be you, since the active player receives priority after a spell or ability resolves.

If you play a land or cast a spell from a graveyard using another permission, it won't stop you from using Coram's permission to do the same thing later in the turn, provided you haven't already done so.

If you play a land, cast a spell, or both using the permission granted by Coram's last ability and then have a new Coram come under your control in the same turn, you can still play a land, cast a spell, or both using the new Coram's permission.

Once you begin to cast a spell this way, losing control of Coram won't affect it. You can finish casting it as normal.

The value of X will change as the greatest power among creature cards in all graveyards changes.

You pay all costs and follow all timing rules for lands played and spells cast this way.