23 Jun 2020
While resolving the triggered ability, you can't pay more than {1}{B} to get more than one Zombie token.
23 Jun 2020
The triggered ability triggers just once, no matter how many creatures died this turn.
23 Jun 2020
If a creature didn't die before your end step begins, the last ability of Liliana's Devotee doesn't trigger at all. The creature may have died before Liliana's Devotee entered the battlefield, however.