Teysa karlov and muster the departed not interacting.
Teysa Karlov states: If a creature dying causes a triggered ability of a permanent you control to trigger, that ability triggers an edition time.
Muster the Departed: Morbid - At the beginning of your end step, if a creature died this turn populate.
A creature dying is the only way for Muster the Departed to trigger, but Teysa doesn't interact with it due to it most likely not being when it happens. However Teysa doesn't state it has to be caused the moment the creature dies so this should fall under what the card states.
My next question is if 5 creatures died would Teysa Karlov trigger Muster the departed 5 extra times?
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Rezzahan#77802 commented
Muster the Departed has an end of turn trigger, it's not a dies trigger. The intervening-if clause is just an additional condition that has to be met to trigger that ability. And no, it doesn't matter how many creatures died, only that at least one did.
A dies trigger is literally happening when a creature dies. The event of a creature dying has to trigger the ability.