"Find your mooring and stop clogging the shipping lanes!"

Dour Port-Mage

Whenever one or more other creatures you control leave the battlefield without dying, draw a card.
{1}{U}, {T}: Return another target creature you control to its owner's hand.

Bloomburrow

"Rations were tightly controlled."
—*Wake of the Beasts*

Bloomburrow Promos

Dour Port-Mage’s first ability triggers whenever one or more creatures you control go to any zone other than the graveyard from the battlefield. They could be returned to your hand, your library, or exiled, for example.

If Dour-Port Mage leaves the battlefield at the same time one or more other creatures you control leave the battlefield without dying, its first ability will still trigger.