Lifelink
Whenever another creature dies, put a +1/+1 counter on Elenda.
When Elenda dies, create X 1/1 white Vampire creature tokens with lifelink, where X is Elenda's power.
If Elenda dies at the same time as another creature, both of its triggered abilities trigger. However, the first one won't do anything since you can't put a +1/+1 counter on Elenda.
19 Jan 2018
To determine how many Vampire tokens are created, use Elenda's power as it last existed on the battlefield.