Drivnod, Carnage Dominus

If a creature dying at the same time as Drivnod (including Drivnod itself dying) causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.

An ability that triggers when a creature "leaves the battlefield" will trigger twice if that creature leaves the battlefield by dying.

An ability that triggers on an event that causes a creature to die doesn't trigger twice. For example, an ability that triggers "whenever you sacrifice a creature" triggers only once.

Drivnod's effect doesn't copy the triggered ability; it just causes the ability to trigger twice. 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 pay a cost for that triggered ability, are also made separately.

If a creature dying at the same time that another permanent you control leaves the battlefield causes a triggered ability of that permanent to trigger, that ability triggers an additional time.

If you somehow control two Drivnods, a creature dying causes abilities to trigger three times, not four. A third Drivnod causes abilities to trigger four times, a fourth causes abilities to trigger five times, and so on. This also means that if you control Drivnod and cast a second one, an ability that triggers when it dies due to the "legend rule" triggers three times.