Echoes of Eternity

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.

If you control two copies of Echoes of Eternity and you cast a colorless spell, each of their second abilities will trigger. Then, each of their first abilities will cause the other's second ability to trigger an additional time. In total, you'll get four copies of the spell in addition to the original spell. If you control three copies of Echoes of Eternity, you'll end up with nine copies of the spell plus the original. Four copies of Echoes of Eternity means sixteen copies of the spell plus the original, five means twenty-five copies plus the original, and so on.

Once an ability of a permanent you control has triggered, making it colorless won't cause that ability to trigger an additional time. Similarly, once an ability of a colorless permanent has triggered an additional time due to Echoes of Eternity's first ability, giving that permanent one or more colors won't remove that additional triggered ability from the stack.

Echoes of Eternity's first ability doesn't copy the triggered ability; it just causes the ability to trigger an additional time. Any choices made as you put the ability onto the stack, such as modes and targets, are made separately for each instance of the ability. Any choices made on resolution, such as whether to put counters on a permanent, are also made individually.

Abilities that apply "as [this permanent] enters the battlefield" or "as [this permanent] is turned face up" are also unaffected.

Replacement effects are unaffected by Echoes of Eternity's first ability. For example, a colorless creature that enters the battlefield under your control with one +1/+1 counter on it won't receive an additional +1/+1 counter.

Abilities that apply "when [this permanent] is turned face up" will trigger an additional time only if that permanent is colorless once it has been turned face up.

If a triggered ability is linked to a second ability, additional instances of that triggered ability are also linked to that second ability. If the second ability refers to "the exiled card," it refers to all cards exiled by instances of the triggered ability.

The copy created by Echoes of Eternity's last ability is put directly onto the stack. It isn't cast, so any abilities that apply "when you cast [this spell]" won't trigger.