My thoughts on builds for Kayn and Raast

Raast: Deals no base damage on ult, just the % HP damage which is physical, lots of heals, is probably more of a bruiser. My personal thoughts is this would be a good build:

and defensive boots of choice, probably

This gives him some decent resistance, a little HP the damage reduction from the dancing weapons, and deaths dance specifically with spirit visage will give him massive amounts of healing. Maw gives a shield that grants more lifesteal, movement speed from deadmans. This should make him a pretty tanky mild damage dealer that can out sustain any tank and go toe to toe with other bruisers.

Kayn: His shadow assassin form passive is key to my opinion on this: for the first 3 seconds when attacking an enemy champion, he deals additional magic damage based on the damage he deals. So, naturally:

and boots of choice.

Phantom dancer in this case is for the combined movement speed of itself, deadmans, and trinity force. Sheen proc/deadmans/and the on hits of blade and wits end (which due to the attack speed hits quite a few times in those 3 seconds) ALL get multiplied by his passive.

Thoughts? This is just my initial observation. Things may change.