On one hand his buffing on red matches makes him ideal for a looper deck, getting bunches of red matches to make him really big.
On the other, losing the turn to cast and kill one troop breaks the loop, so if you want to cast you need to clean up the board of all match 4+ (likely losing all the mana since your troops are full), then cast once, give turn to AI, then start looping again to refill.
If he had "If the enemy is killed, gain a turn", even at the old 3:1 ratio, he would fit FAR better into a loop deck.
The other option is to try and use him as a skull damage dealer with something like:
Never intending to cast the bull (unless just one troop left to finish), cycle cat/alchemist to build, then Courage on red+skulls to dish damage. But Ketras' blocking red to alchemist makes it slow to get going and generally inferior to faster attack builds with either Dragon Soul/Krystanax or Kraken/Spider/Valk/Mab or Bone Dragon/whatever