Ulora Tandril, Death Dealer

When Ulora Tandril enters the battlefield, you may sacrifice a creature, if you do, put X +1/+1 counters on Ulora Tandril, where X is the sacrificed creature's converted mana cost.
At the beginning of your upkeep, you may put up to X 1/1 black skeletal dog creature tokens onto the battlefield, where X is the amount of +1/+1 counters on Ulora Tandril, if you do, skip your combat phase.