Not sure how to search for highest HP wins, but it was fun to try and get a quick win where I'm trying to get as high an HP pool as possible.
Character - Level 27 Oni in Dragon Form with 27 Fighting, 27 Invocations using Elyvilon's Divine Vigour and Berserk Rage.
Started Gladiator to focus on bashing people until I was ready to invest in Shapeshifting, ended up being very easy run. Walking around in Statue Form and using Divine Vigor had me fighting most tough fights with about 630 hp, which is just too much for most encounters to actually deal with. Also had Arga and 48 Str most of the time, so I was hitting very hard to boot.
Only improvements I can think of would be to find some rings of the Octopus King dude with +2 HP and the +% hp mutations.