Elesh Norn, Mother of Machines

Elesh Norn's second and third ability each affects a permanent's own enters-the-battlefield 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, such as For Mirrodin!

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

Elesh Norn's abilities don't look at who controls the permanent entering the battlefield, only who controls the permanent that has the triggered ability. For example, if you control Elesh Norn and a permanent with the ability "Whenever a creature enters the battlefield, you gain 1 life," a creature entering the battlefield under an opponent's control will cause that ability to trigger twice.

Replacement effects are unaffected by Elesh Norn's abilities. For example, a creature that enters the battlefield under your control with one +1/+1 counter on it won't receive an additional +1/+1 counter.

Similarly, a permanent entering the battlefield at the same time as Elesh Norn (still including Elesh Norn) won't cause abilities of permanents an opponent controls to trigger.

Abilities that apply "as [this permanent] enters the battlefield," such as choosing a card type with Stenn, Paranoid Partisan, are also unaffected.

In a Two-Headed Giant game, Elesh Norn does not affect triggered abilities of permanents your teammate controls.

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.