Not sure if I understand correctly but sacrifice kills the last spot and then Krystenax summons into that spot
I use something with magic link to get sacrifice started quicker but mercy is good too. Or dragotaur which has a chance of summoning a dragonette when he's killed. My team is:
Unicorn banner (+2 purple +1 yellow)
I only take it out against super weak opponents though! A more viable PvP team would have Krystenax at the top and no dragon eggs - possibly another Krystenax instead.