Replacement effects are unaffected by Starfield Vocalist’s first ability. For example, a creature that enters the battlefield under your control with a +1/+1 counter on it won’t receive an additional +1/+1 counter.

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” 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.

Starfield Vocalist’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.

Starfield Vocalist’s first ability affects a permanent’s own “enters” triggered abilities as well as other triggered abilities that trigger when that permanent enters the battlefield. Such triggered abilities start with “when” or “whenever.” Some keyword abilities also include a triggered ability that happens when a permanent enters the battlefield.

If you control two Starfield Vocalists, a permanent entering the battlefield causes abilities to trigger three times, not four. A third Starfield Vocalist causes abilities to trigger four times, a fourth causes abilities to trigger five times, and so on.

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

Abilities that apply “as [this permanent] enters,” such as Famished Worldsire’s devour land ability, are also unaffected.

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.