Be very wary when exploring Elven Halls.
I cleaned every floor, minus the last one (as considering what i experimented so far in the "easy floors", i'm sure my character is going to die if he goes on the last insane floor).
Because of past experience, my fighter was wearing a Ring of Life Protection.
He entered Elven Halls at level 23.
He cleaned floor 1 to 6 surprisingly easily as i was lucky none of the deep elves summoners i encountered were in open space, so it was easy to kill them before they created too much demons.
Greater Self Healing from Elyvilon is one of the greatest thing ever, can't believe i overlooked that god for so long maybe explaining why my fighting characters die so easily
this power alone saved my character an insane amount of time, no way he would have reached level 23 otherwise.
And use it once and a very lot of experience goes into it, making Invocation climbing up very quickly (and so can heal you even more).
30 AC definitively help too.
Thanks to bunch of luck i have an amulet of the gourmand and a ring of sustenance, so i have no more care about hunger and can then use those healing powers more easily (as they increase hunger like everything in Crawl anyways).
I have found an amulet of Rage that has saved my character from some Lair level too and always keep it just for very difficult case.
But from past experiences, no way i would go to floor 7 of Elven Halls, as i remember what kind of enemies to expect, no way my character could survive at level 23 especially with the kind of monsters the high level deep elves that are encountered only in Floor 7 can summon... if i kept level 23.
Because once i finished cleaned floor 1 to 6, my character reached ... level 20.
Yes, despite wearing a life protection ring cleaning those 6 floors made my character lose 3 levels !
And insane amount of experience gone with the absurd amount of draining weapons and spells that apparently thanks to bad luck my ring didn't protected me from.
I guess you need 2 life protection ring then to be sure of not being experience crippled in Elven Halls. But again need tons of luck to find a 2nd ring, as in the insane amount of time i spent with this character i found only 1.
Will take a lot of time to get back to level 23...