Mashup of Wormfang crab + Face Trader.

Also, what is "wormfang"? Dragons are wurms, right? So this is a worm as in an earthworm, with a giant tooth? There are half a dozen wormfang creatures, all blue, with a "when this enters, exile/skip/pay something, when it leaves, get it back". Why does "wormfang" mean "temporary additional cost"?

The key part you missed about the Wormfang creatures is that they're all Nightmares, and all from Judgment.

Nightmares premiered in Torment when they were black and exiled opponents' stuff, like Faceless Butcher and Mesmeric Fiend. Torment, you'll recall, was "the black set", where there were more black cards than usual, fewer green and white cards, and where blue and red were especially black-friendly.

The next set was Judgment which reversed things: few black cards, more green and white cards, and blue and red are repenting for having allied with those nasty black cards. So blue and red got "reverse Nightmares" that exiled your own stuff. Blue got Wormfang Crab, Wormfang Manta and so on; red got Petradon and Petravark, and Spellgorger Barbarian and Soulgorger Orgg and Worldgorger Dragon.

Ah! You're right, I had forgotten or never known most of that, and it makes the judgement nightmare creatures make a lot more sense.

But what I still don't get is the connection between "what shall we call blue reverse-nightmare creatures in the judgement block" and "I know, 'wormfang'"...? :)

Heh. That I'm afraid I cannot answer :P