Panharmonicon

Replacement effects are unaffected by Panharmonicon's ability. For example, a creature that enters the battlefield with one +1/+1 counter on it won't receive an additional +1/+1 counter.

If an artifact or creature entering the battlefield at the same time as Panharmonicon (including Panharmonicon itself) causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.

In some cases involving linked abilities, an ability requires information about "the exiled card." When this happens, the ability gets multiple answers. If these answers are being used to determine the value of a variable, the sum is used. For example, if Elite Arcanist's enters-the-battlefield ability triggers twice, two cards are exiled. The value of X in the activation cost of Elite Arcanist's other ability is the sum of the two cards' mana values. As the ability resolves, you create copies of both cards and can cast none, one, or both of the copies in any order.