Ob Nixilis, Captive Kingpin

Ob Nixilis's last ability looks at all combat damage dealt to an opponent in total to determine whether it triggers. For example, if three 1/1 creatures deal combat damage to an opponent, that player loses 3 life. Ob Nixilis's ability won't trigger.

Playing the card exiled with Ob Nixilis follows the normal rules for playing that card. You must pay its costs, and you must follow all applicable timing rules. For example, if the card is a creature card, you can cast that card by paying its mana cost only during your main phase while the stack is empty.

If you don't play the card, it will remain exiled.