Mind-Cage Oni

Description
Sentinel: Spell cast. Whenever your opponent casts a spell, put a copy of that spell into your action bar.

Spell Interactions
In general Spell Sentinel interactions follow these rules:
 * If your spell targeted a spell sentinel directly with a destroying effect, it WILL continue its effect past the transformation. Like Natural Selection, Martyrdom.
 * If your spell targeted anything else - a Wraithling, a tile - anything - the spell will fluff. See Ritual Banishing. This manifests in strange ways - Ritual Banishing just loses its target and does nothing.

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

Seeking Eye (Starhorn BBS)
If you have an unflipped Mind-Cage Oni on board and 1 empty space in hand, and the opponent casts Starhorn's BBS, you will draw a card first and then mill their BBS. However, if your Oni is already flipped, you will get their BBS in hand and mill the card you draw.

Ritual Banishing
If a Ritual Banishing destroys the Watchful Sentinel, the Watchful Sentinel will get destroyed, flip and a Mind-Cage Oni will take its spot. Its owner will get a copy of Ritual Banishing.

Chromatic Cold & Sun Bloom
Chromatic Cold and Sun Bloom transform and dispel the Sentinel. Therefore they don't give Mind-Cage Oni's owner a copy of the spell (unless it was already transformed).

Balance Changes

 * v. 1.87 - added with the Unearthed Prophecy expansion.
 * v.1.96 - Stats changed from 4/3 to 3/2