During combat, creature cards in graveyards can attack and block just as if they were on the battlefield. Attacking creature cards in the graveyard can be blocked only by creature cards in the defending player’s graveyard.

Creature cards in graveyards can attack planeswalkers on the battlefield.

Other combat-relevant abilities such as flying work on attacking or blocking creature cards in graveyards. An attacking creature card with flying in a graveyard could be blocked only by creature cards with flying or reach in graveyards.

Over My Dead Bodies allows you to attack or block with creature cards in your graveyard. If you do, for the duration of combat, the attacking and blocking creature cards are treated as if they are creature cards on the battlefield which means they can be affected by spells or abilities that would affect creatures on the battlefield. That means, for example, if you have a Lord of Accursed on the battlefield (“Other Zombies you control get +1/+1”), all your attacking and blocking graveyard creatures (which Over My Dead Bodies makes into Zombies) would get +1/+1 while in combat.

As you choose attackers or blockers, check whether state-based actions would immediately remove any of them from the battlefield. If so, those creatures can’t attack or block, as appropriate.

Creature cards in graveyards attacking or blocking will cause abilities that trigger whenever a creature attacks or blocks to trigger.

You can target attacking or blocking creature cards in graveyards with spells like Giant Growth.

If an attacking or blocking creature card is destroyed by a source without undeathtouch, such as Murder, it stays in the graveyard but is removed from combat.

If Over My Dead Bodies leaves the battlefield in the middle of combat, graveyard creatures go back to being just dead. They’re removed from combat.