What happens when more than one creature dies causing a trigger

Question

Overseer of the Damned is a creature with the ability "Whenever a nontoken creature an opponent controls dies, put a 2/2 black Zombie creature token onto the battlefield tapped"

Now, lets say 3 of my opponent's creatures die simultaneously, either through combat, spells, or sacrificing. Could I put the triggered ability on the "stack" so to say in order to get 3 2/2 black zombies (one for each non token creature that died that my opponent controlled), or am I forced to put one and only one despite 3 creatures dying?

Answer 1

If an ability triggers each time a creature dies, then it triggers once for each creature that died, not just for each event where one or more creatures died.

Rule 700.1 says

Anything that happens in a game is an event. Multiple events may take place during the resolution of a spell or ability. The text of triggered abilities and replacement effects defines the event they’re looking for. One "happening" may be treated as a single event by one ability and as multiple events by another.

in addition, rule 603.2c says

An ability triggers only once each time its trigger event occurs. However, it can trigger repeatedly if one event contains multiple occurrences.

In this particular case, that means that even though the creatures died at the same time, they count as different events for the purpose of triggers that look for individual deaths.

Answer 2

Overseer of the Damned would trigger 3 times and you would create 3 2/2 zombies when those triggers resolved.

There are a few different ways that triggers are scoped in magic, I'll look at three of them here that all create 2/2 zombie tokens. I put the trigger in italics and what the trigger is watching for in bold. First we have the example here for Overseer of the Damned:

Whenever a nontoken creature an opponent controls dies, create a tapped 2/2 black Zombie creature token.

Second we have Curse of Shallow Graves (There are no death triggers with wording like this):

Whenever a player attacks enchanted player with one or more creatures, that attacking player may create a tapped 2/2 black Zombie creature token.

And third we have Doomed Dissenter:

When Doomed Dissenter dies, create a 2/2 black Zombie creature token.

The difference is what they watch for, how broad or narrow. Overseer of the Damned is the most broad, watching every creature (that fits criteria), so when any of those creatures die, it triggers for each creature, so you create 1 zombie per creature. The second example watches for "one or more" creatures. It doesn't care if it was 1 creature or 100 creatures, it will only trigger once and create 1 zombie. The third references the card by name, so it only watches itself, and will only create 1 zombie.