Hearthpwn

Compare with Righteous Defense they are very similar.  That undead restriction might be an issue though.

It could also be a strength by making sure that it hits the correct minion.  That does limit it's use somewhat though.

Quote from ShadowAldrius >>

No one ever played Assassinate or Blastcrystal Potion specifically because they were overcosted for what they did.

 I remember Renolocks running blastcrystal back in the day and even 6 mana siphon soul. Neither were run in mine, however.

To be fair, it's Blastcrystal Potion being more of a badly balanced card than Twisted Tether being power creep. that card blows. 

Blastcrystal wasn't badly balanced.  It was used quite often back in the day.  It's a sign the game is powercrept to hell.

Blastcrystal Potion Huge powercreep

So it's like a worse version of Righteous Defense, but should still be okay.

yeah, people really don't see it for some reason. 33% increase in cost to kill a 1/1 is not that great. But probably still better than siphon

wait, warlock got 4-cost removal that doesn’t have a collateral damage effect? no mana crystal broken or pay life? what a miracle!

Holy powercreep

the theme of this expansion: mixing all the class identities randomly

also power creep at its finest. back in my day 4 mana destroy anything had to have some drawback with it.

Blastcrystal Potion cries in the corner

Yeah.. For the longest time, when they launched new cards with effects similar to older cards, they always had some drawback  or some kind of compromise in order to not be just straigth up better, like that Consecration version for DKs (Remorseless Winter), where it also draws a card, but its a rune card to compensate. Now this Twisted Tether is just a prime example of powercreep, cause not only it doesn't have any drawback like Blastcrystal Potion, it has a huge plus. 

Well, if no one runs Siphon Soul anymore, then it's pretty obvious that you need something better to replace it.

No one ever played Assassinate or Blastcrystal Potion specifically because they were overcosted for what they did.

No one played Assassinate because why would Rogues want to kill a minion when instead they could kill their opponent? It just didn't fit Rogue's plan. Giving up a mana crystal is terrible, that's why Potion wasn't played.