Red Kayn Scaling

If you like stuff like this, try a stacked AD Illaoi. She sits back, and rips spirits that have 90-almost 100 percent damage-to-enemy conversion. It's not even close to viable, but fun when it works out.

Well, in a case like this, he becomes the perfect counter to all non-Darius / Cho'Gath tanks (Darius b/c in an extended trade his ult will slaughter Kayn, and same for Cho; in theory you may be able to outsustain Nasus, if you have high enough AD).

A single Q will full heal him, and deals some 40% max health physical damage (if both parts hits) at this much AD.

In general, you want to stack two AD items on Kayn early, and then into full tank (AD jg item and DD/Ghostblade for example), or into semi tank items, depending on needs. I will usually take BC instead of DD or Ghostblade if vs heavy tanks (Sejuani, Rammus, Nasus), and if vs mainly squishier tanks I'll take the increased lethality so that I can keep my advantage.

I tend to view it as, pick blue Kayn if you want to blow up the squishies, red Kayn if you need to face their bruisers and tanks.

I'd never stack full AD like this in a regular game, unless I had to (there are some games where it's all or nothing and you need the % health to cut through the tanks more than you need to be tanky).

Depends largely on player skill, knowledge, farm, and current status of the game. I wouldn't build a Duskblade while behind on red Kayn, though I might if I were versus mainly Assassins (and wanted the CC that red offers). Correct pathing (avoiding enemy wards, not just in lane phase but throughout the match to surprise people), proper build paths, and just general awareness would let this build stay pretty viable. For example, using a sweeper to verify you're not being seen, and then hiding in a bush, in their jg, to surprise and oneshot the enemy ADC or similar carry.

Blue Kayn will hit harder, but has less survivability and will struggle vs bruisers/tanks, so it's a trade off depending on what you want.