I cant really teall because Ive had games where I felt unkillable and really strong, but Ive also had games where I just got kited, did no damage with both 
and 
and went oom before I could kill anyone.
Ralanr1 votesSo far I've seen people comment that he heals too much in his Darkin form. I haven't seen him do good that often so idk.
Rockm Sockm1 votesHe can be a very strong bruiser pseudo tank for top lane.
Rhaast seems balanced around the fact he weak early comparatively. He excels in extended team fights but can easily be c/c and bursted.
He has plenty of counterplay built into his kit.
I have been going DD into black cleaver as well. I haven't settled on the best tank items to compliment.
BLACK REALM GOD1 votesmy personal opinion is that the shadow kayn is stronger than darkin rhaast. it depends on what enemies you're facing though. if you're playing as rhaast you can deal massive damage to high hp enemies. finding those enemies is unlikely since most games only have 1 champion with over 3k hp. the knockup is strong, but what rhaast gains in life he loses in pure damage.
also you're buying the wrong items. kayn is an assassin. when you turn him into rhaast he becomes a fighter. as shadow kayn he's an even stronger assassin.
in order to get the most out of kayn and rhaast you're going to need lethality and cooldown reduction. not hp and lifesteal. if you want damage go with infinity edge and triforce.
i also recommend getting a small amount of armor and magic resist because his base stats for both of those are pretty low considering his base attack speed and his reliance on his abilities. after you get your abilities though and some physical damage you're golden.
you need to be able to kill your opponent within this combo W Q 1-2 basic attacks R. if you cant then you shouldnt go in.
FireDrizzle2 votesInfinity edge isnt strong without other crit items though, and he does a lot of damage with abilities.
I went in the practise tool and the only way to get good dps with crit was 
(which would be painful to build early on) . An ad heavy crit build did no damage, so infinity edge on its own looks dubious..
BLACK REALM GOD1 votesyou need to build lethality items. infinity edge or essence reaver. you dont need blade of the ruined king.
try this one.
a combination of 3 of these and your favorite boots, armor, magic resist, and your smite item. then the cunning mastery line that grants health back for killing an enemy. storm raiders surge to get away. should be 12 18 0 or 6 18 6.
maw makes for an okay magic resist item, but nights edge can provide extra kill potential if you use it while wall walking towards a wounded enemy.
FireDrizzle2 votesI was interested in trying that build I wrote down but I acknowledge building it will feel painful so it wont be strong.
Kayn has cast times and no attack speed steroids or ad boosts, I think crit is a bad stat itself on him. Infinity edge on its own wont be strong 100%, its like building rab as the only ap item in a build.
BLACK REALM GOD1 votesit's the most damage you can get for a single item at its price range. you dont need to critical. it's like a soraka 1% critical rune. you get it for the raw stats (the 70 AD) and then when you critical you benefit additionally from it.
most damage to least damage
and then everything else is 50 damage or less. you dont need the lifesteal cause like you said you cant stay in a fight long enough to sustain through it. after 1-2 spell rotations you're dead. cooldowns are short, but not so short that you feel like you're in urf mode and his attack speed is low. all kayn and rhaast need is raw damage and lethality. rhaast can use deaths dance, but the price tag makes it so that you're building it later rather than sooner. due to kayn not having the built in sustain that rhaast has and you need that penetration from lethality. youmuus is a great first item.
i've seen phantom dancer builds, but honestly the attack speed, movement speed, and critical strike chance are wasted. and even more than that the passives are pointless because kayn can walk through walls and doesnt build enough hp to make lament useful.
infinity+triforce does quite a lot of damage. kayn has pretty high base damage. it's expensive though, but as a jungling assassin with an execution R you should have plenty of gold.
Zopiloth1 votesI played Rhaast with those items, was 4 2 4 got into a 2v5, the moment I was about to die I ulted a rammus, and got all my Hp back, when my ult was over all the enemy team was trying to kill me and I used my W and Q, from 10% hp I went to 70% and then my team killed everyone.
Yeah, Rhaast is a fucking monster, since I had grevious wounds all the time that teamfight went on.
By those items I mean BC and DD.
