If Dunerider Outlaw dealt damage to an opponent who later left the game before that turn's end step, its ability still gives it a +1/+1 counter.
19-03-2021
wotc
Whirling Dervish's triggered ability gives it at most one +1/+1 counter each turn, regardless of how many opponents were dealt damage beyond the first.
19-03-2021
wotc
Whirling Dervish's triggered ability checks to see if it dealt damage during the turn to an opponent of its current controller. If it dealt damage to player A, then player A takes control of it, the ability doesn't trigger.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.