23 ways to increase hp :

costumes all 5 pieces gives plus 500hp
merac castle siege constitution potion gives 15 constitution points
constitution potion gives 15 constitution points
halloween jawbreaker or round candy gives plus 300hp
p1 pet gives plus 400hp
high levels armors gives 400hp bonus each
all stat points in constitution (+3 hp per +1 stat point in constitution, night shadow is +2.1hp)
topaz level 5 + garnet level 5 (plus 1000hp each garnet, each topaz gives +5% constitution) in all armor and weapon
and asking too much : use all 3 accesories 5 seals each whit 8 constitution and/or 56 hp
use afs to upgrade hp seal (3*5*(24 constitution and/or 275 hp))
double life level 3 (now is plus 10000hp)
candies gives 20%hp
jinar stones gives 5000 hp
high plused armor +28 (+100hp each plus past +10)
all 3 hp boosters at the same time (6000hp+2500hp+2000hp)
bless arrow level 5 skill of archer gives plus 5000hp
scream of warmaster level 4 skill gives plus 3000hp
archer soul +15% all stat points
cleric soul +5% all stat points
think there is some armors that gives +10% hp each
if u are a specialist use earth bless skill level 4 gives plus 1867hp (466.666hp*4)
be level 185 (average +30 hp per level)
and almost impossible use title "last chaos newbie" (+10% hp)
plus more things that give hp and i forget to write

now whit new patch hp, let see what is the maximun hp possible for each class
post screen shot at least 50k hp +

and please tell me if i forget something that give more hp