If Arwen, Weaver of Hope and another creature you control enter the battlefield at the same time, Arwen's ability won't cause that creature to enter with additional +1/+1 counters on it.
16-06-2023
wotc
To determine how many additional +1/+1 counters a creature enters the battlefield with, use Arwen, Weaver of Hope's toughness as that creature is entering the battlefield.
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.