If you're a melee with too many feats (mainly fighter, lesser extent monk) and are wondering how to self heal... You may want to trade a feat for Magical Training and twist in cocoon.
I did it on a whim when I LR'ed my monk/fighter from Str based to Wis based, and it has been working great. I had half expected that I'd just swap it on another toughness feat after playing with it for a bit, but I'm keeping it. What is really ideal is that Magical training gives you Echos of power, so if you are even below 12 SP, it brings you back to 12, which is the cost of cocoon. It takes only 18 seconds to go from zero to 12, so you can use 3-4 cocoons a minute perpetually.
Not only is the 150 temp HP for 9 seconds useful, but it is a big chunk of healing. As a helf monk, I tend to have decent Healing Amp, but slotting 100 Devotion would accomplish the same healing I get (about 150-200 total). (I carry around a devotion trinket, but don't bother using it that often.) It isn't even just self healing either, I've hit others with it, and unlike most similar tricks, it gives a buffer to Pale Masters who need it (although the healing doesn't work).
It is enough self healing to get me through an EH quest all by itself, and is a nice boost to survivability in EE.
To be honest, I also have Cleric Dilly. Part of me thinks I should switch to Rogue dilly since I can use this for self healing.... but the other part still loves 30 resist wands, restoring neg levels, res scrolls... and I do still use the almighty heal scroll, just far less than I used to.
Earlier today I dealt with the Stormreaver on EH while the rest of the party took down the dragon. I'd hit myself with Cocoon whenever I was about to go Boom, and it kept my HPs at a nice comfortable level with no divine helping me. (Only scary parts were due to someone else getting close enough that I'd get a rebound boom.) Of course, I would then healscroll myself back up.... but without it, I'm sure at least one of those double booms would have gotten me.
In EE I've found it to be very synergistic with heal scrolls. Without Cocoon, when under fire it is very hard to get a Heal scroll to stick even with a monk's concentration. But cocoon/scroll as a 1-2 punch works pretty much every time.
Anyone else ever try this?
If not, perhaps you should. How many toughnesses do you need anyway? I used to keep Healing Spring as a twist instead. And sure, it is great and all, but the only 1 charge and it stops if you die makes cocoon way more useful over an entire quest than Spring.