"Atraxa, Grand Unifier" is currently one of the most (if not the most) annoying card to face in standard. The issue is that the card does too much :

1_ creating an incredible amount of CA (up to +8)
2_ The CA is not a Draw so it is not punished by Sheoldred, Faery mastermind and similar cards.
3_ The ETB triggers independently of how the card comes into play. Even blinks works on it. You can create a copy just to trigger the ETB if you fancy.
4_ The cards stats are awfully high (better than any multicolor creature of CMC 7 in MTG arena).

Please just Ban the card.