6/6 for 4 (or 12/12 for 6) seems awesome.
Ability to fight at-will for 3 is really awesome.
Crap
Phantom ability is Crap. I mean,
Witherscale Wurm was never good. It couldn't be used as controlled removal, but it was really, really not good so that isn't a lofty standard. Since it can recur, dead Poluk does have something going for it, but the exile six part of Escape is going to put a limit on how often you can really do it. This isn't a combo card where you can just mill your whole deck to chain it again and again, it seems best in a sort of control shell that I think could use the resources spent to fill yard and the resources binned better. It's not terrible even if you assume you're only getting two hits, because it will probably trade for sizeable CA fighting, but... I don't see it going anywhere impressive.
However, I do like cheese, and my cheese senses detect
Scythe of the Wretched and
Vampiric Embrace. Scythe lets him reset himself by self-fighting and steal things in the meantime. Re-equiping the blasted thing would get mana expensive, but if he's your commander it seems legit.
Vampiric Embrace, though, is really extra funny because it allows a hack of the classic Phantom cheese. Slam Embrace on Polukranos here and he has +2/+2, flying and gets a counter whenever he kills something, which he can do on command by fighting for cheap. As long as he has one counter and a toughness boost (like the +2/+2 from Embrace) he physically cannot be defeated since overflow damage doesn't go to his toughness, it's all prevented. So you can get in a cycle wherein he fights something, loses his one +1/+1 counter, but then gets it right back from killing the thing he fought. With just the Embrace, his reach isn't very high; you have to pick on things with 3 toughness or less or you will take real damage. But come on, there are other auras, there's equipment, amping his killing potential without using the expendable +1/+1 counters isn't the hardest thing in the world. Honestly, I would be very tempted to try and do this in EDH if Vampiric Embrace was not literally the only card that would let me do it in one. I could get his "and refund a counter" up with
Blade of the Bloodchief,
Sadistic Glee, or
Eternal Thirst but none of those let him survive on 0 counters for long enough for the trigger to resolve. Now, toughness-boosting enchantments and equipment are not genuinely hard to come by, but if I'm going to build a commander deck around a cheesy interaction I really do want to be able to set it up at least in a starting form with some sort of reliability. So I probably won't do this one... but it does still seem fun.