Grothama, All-Devouring

Other creatures have "Whenever this creature attacks, you may have it fight Grothama, All-Devouring."
When Grothama leaves the battlefield, each player draws cards equal to the amount of damage dealt to Grothama this turn by sources they controlled.

Bloomburrow Commander

The List

Battlebond

Creatures fight Grothama before blockers are declared. Any creatures that die in the fight can't be blocked. Any attacking creatures that survive the fight will still be attacking, may be blocked as normal, and will deal damage to the player or planeswalker they're attacking if unblocked.

Grothama's last ability triggers even if it dies without being fought by attacking creatures. For example, if you use Blaze to deal 10 damage to Grothama, you draw ten cards.

If multiple creatures attack, each desired fight happens individually in the order the attacking players choose. Once Grothama has been defeated, any remaining attacking creatures can't fight it.

The controller of the attacking creature chooses whether that creature fights Grothama.