Xerroloth

Description
Sentinel: Spell cast. Whenever your opponent casts a spell, put a 4/4 Fiend into your action bar.

Daemonic Lure
Daemonic Lure on a Spell Sentinel deals one damage and then flips the Sentinel which will have full health afterwards.

Chromatic Cold & Sun Bloom
Chromatic Cold and Sun Bloom transform and dispel the Sentinel. Therefore they don't give Xerroloth's owner a 4/4 Fiend.

Ritual Banishing
If a Ritual Banishing destroys the Watchful Sentinel, the Watchful Sentinel will get destroyed, flip and a Xerroloth will take its spot. Its owner will also get a 4/4 Fiend.