If this card was Tribute Summoned by Tributing a DARK monster, instead of targeting 1 card on the field, you can target 2 cards. (When this effect is activated, you decide whether to target 1 or 2 cards.)
"banish it" and "inflict 1000 damage to your opponent" are considered to happen simultaneously. If the banished monster was a DARK monster, the last thing to happen when the effect resolves is "banish all cards with that name from the hand, Main Deck, Extra Deck, and Graveyard of the player who controlled it.".