Update: okay, now I'm totally puzzled. I had a Tartarian Titan boosted to S9 with items (which is the same as the above-described kraken, S8 kraken + Crystal Coin = S9) scripted to <Master Enslave> and that's it. She had exactly 8 pearls. She cast the spell, no problem, and ended with 200 fatigue. So I see no reason why the kraken should not have cast its master enslave.
If it makes any difference, I'm running on Windows. This is a weird situation.
Edit: my only idea so far is that perhaps the kraken decided it wasn't "worth" burning 8 gems. My Tartarian Titan was in the company of several other Titans all decked out, and she had +3 Penetration from items, and the army we were facing was Ulmish. When she cast the spell I got about 65% of the enemy army. The combat AI simulates everything before it actually commits to a choice, and perhaps in the simulation (since the Kraken had only +2 Penetration, and depending upon the MR of the enemy troops) only a few enemy were controlled. Since the kraken was apparently on its own, perhaps the AI decided it didn't want to burn 200 fatigue just to control 10% of the troops. My other theory is that the kraken, as a melee SC chassis, somehow has different behavior than a mage chassis. I don't really believe either of these theories, though. If you ever figure out what was going on, though, please let us know.
In the meantime I'm having fun knocking down castles with my Ulmish army. The computer always builds these armies of 400+ troops, but I've never actually *owned* one before...
-Max Wilson