Great concept, very flavorful. Unfortunately, it's just not cost-efficient at all for what it does.
Perhaps if it was something like:
At the beginning of your upkeep, put a pin counter on Voodoo Doll. {T}: Voodoo Doll deals X damage to target creature or player, where X is the number of pin counters on Voodoo Doll. At the beginning of your end step, pay {X}{X}, where X is the number of pin counters on Voodoo Doll. If you don't, sacrifice Voodoo Doll and it deals X damage to you.
This still makes you pay XX once per turn or lose the doll and take damage, but it allows it to combo with untappers, and lets you get a use out of it in a turn where you can't or don't want to pay.
Comments (6)
.....Well, hey, it's still better than Rakalite!
Perhaps if it was something like:
At the beginning of your upkeep, put a pin counter on Voodoo Doll.
{T}: Voodoo Doll deals X damage to target creature or player, where X is the number of pin counters on Voodoo Doll.
At the beginning of your end step, pay {X}{X}, where X is the number of pin counters on Voodoo Doll. If you don't, sacrifice Voodoo Doll and it deals X damage to you.
This still makes you pay XX once per turn or lose the doll and take damage, but it allows it to combo with untappers, and lets you get a use out of it in a turn where you can't or don't want to pay.