The upped one isn't much of an upgrade. It doesn't get more of a bonus than the normal version, and its special ability generated less of a bonus for itself (Although Elite Skeletons are more powerful) The special ability looks of limited use as well. You would only want to get rid of a Bone/Ivory Dragon is when it is about the die. You gain 8 damage with the unupped while losing 10. With the Upgrade, you gain 9 damage and lose 11. The only point where that is useful is if the dragon is about to die anyway. You would need a Bone yard to get the sacrifice to even equal the loss of the dragon.
I think a different special ability is in order for it. Perhaps something that increases the effectiveness of it's creature control abilities.
Maybe an ability that multiplies the poison counters on a creature by 2? Speeding up the accumulation of poison greatly.
Maybe an ability that deals the poison damage now instead of during the opponents turn? Since the best CC is about killing important creatures NOW instead of later.
If you still want another Death Effect activator, maybe a passive ability that triggers death effects whenever the opponent player is damaged?
If you still want to sacrifice, maybe sacrifice a skeleton to increase health? Basically drain attack power to increase health.
I love your set. I hope it goes far.