Collectible Card Game Headquarters

Describe the bug:
Thick-Skinned Goblin doesn't let you pay rather than Deepcavern Imp's echo cost.

Which card behaved improperly?
Deepcavern Imp. (Or Thick-Skinned Goblin, see below.)

Which update are you using? (date, name)Which type? (duel, gauntlet, sealed deck)
df88666 from 2017 Dec 14.

What exactly should be the correct behavior/interaction?
Ruling: 9/25/2006: When an echo ability you control resolves, you have three options: pay the echo cost, pay , or sacrifice the permanent.

Thick-Skinned Goblin doesn't actually ever do that; instead, you can only sacrifice the permanent or pay nothing (not even , on the off chance something's increasing the cost). So the real problem's with Thick-Skinned Goblin instead, if you want to be pointlessly nitpicky.

Are any other cards possibly affected by this bug?
Skizzik Surger would be, if it were in Manalink.

Shah of Naar Isle works ok, but only by accident: it's not implemented as an echo cost at all, but it has a ruling that it still triggers anyway if you use Thick-Skinned Goblin's ability with it.

Also you don't get a chance to even pay nothing with Thick-Skinned Goblin in play if you don't have the available mana to pay the echo cost creature gets sacrificed immediately.

Fixed only that it didn't honor Thick-Skinned Goblin the way normal echo did.
No pay 0 cost nor the bug I mention directly above.