When Emissary of the Sleepless enters the battlefield, if a creature died this turn, create a 1/1 white Spirit creature token with flying.
4/8/2016 Emissary of the Sleepless’s last ability checks only if a creature died earlier in the turn. The creature card doesn’t need to still be in the graveyard.
4/8/2016 Token creatures that are destroyed or put into a graveyard from the battlefield for other reasons do die—they go to their owner’s graveyard before ceasing to exist.
4/8/2016 Emissary of the Sleepless’s last ability doesn’t create additional Spirit tokens if more than one creature died this turn.