Right now, this is Metamorphosis.
You transform into a Demon for 30 sec. This form increases your armor by 600%, damage by 20%, reduces the chance you’ll be critically hit by melee attacks by 6% and reduces the duration of stun and snare effects by 50%. You gain some unique demon abilities in addition to your normal abilities.
I have a better idea. My version costs, say, 35% of base mana.
Transform into demon form, increasing damage by 30%, armor contribution from items by 600%, reducing the chance you’ll be critically hit by melee attacks by 10%, and reducing the duration of stun and snare effects by 50%. You gain some unique demon abilities while in demon form, and your spellpower will be applied to your melee attacks. Your controlled demon is unsummoned while in demon form, but you retain any benefits gained from Demonology talents.
You’ll notice something missing: duration. Here’s why: I think Metamorphosis should work more along the lines of, say, Dire Bear Form. Frankly, as a 51-point talent, I feel we should be able to stay in freaking demon form as long as we want. Taking the demon away seems fair, since theoretically the demonologist’s damage will make up for the loss of a demon in this form, and the demonology talents still apply, such as the effects of Master Demonologist. Hell, if Metamorphosis worked like this, then this might actually create a reason for demonologists to use Demonic Sacrifice! Oh – and I’d get rid of Challenging Howl, and re-add Shadow Bolt Volley. Seriously, warlocks shouldn’t be tanking.
Man, I can hear the cries of “OP!” and “nerf warlocks!” already… :)