Entropy is worth remaking. The problem with it is that it's very pricy and it gives only damage, but not nearly as much overall as say IE. It would be nice if it gave say a bit of crit chance.

I've built Kitae before, I don't think I've ever built an Entropy, and Riven is one of my 'mains'.

You're just better off with Brute -> Mallet/Sang -> Malmort (depending)

Please don't give Entropy Crit, make it more of a focused AD caster item.

Entropy is amazing, and its a good replacement for red buff. The very concept of "Phage + BF Sword" is ridiculous, if nothing else.
Kitae's is an item that SHOULD be good, and can even be cost-effective when the enemy manages to stack somewhere above 2.2k HP, but the real reason why it falls apart is because it:

A) It is compared to Wit's End. Even though Kitae's has scenarios it can be superior to Wit's End, people look at the two items and say "Which of these do I want? Wit's End of course, this is the quintessential Tanky-DPS AS/MR Item in the game. I CANNOT go wrong buying this."

B) Quite simply, it just doesn't feel like it shreds. It's a shredding item but you don't FEEL like a cheesegrater when you buy Kitae's. Your damage goes up, but that happens when you buy other items too. The impact upon the player is unimpressive.

C) Wit's End has a distinct player-perception advantage from Summoner's Rift, it is recognized in the Meta as being infallibly viable and even was nerfed without losing any popularity whatsoever. It has a place in people's hearts and minds, and this will influence player thought. Kitae's Bloodrazor on the otherhand is "new" and has a strong association with Madred's Bloodrazor, and the negative perception of this item being incredibly cost-inefficient and a "trap" that the Almighty Theorylord Xypherous had to descend upon Valoran and strike it from the shop forever. This is not the "social-meta-perspective-environment-thingy" conductive to opening one's arms to it.

Thusly; I arrive at the conclusion that Kitae's Bloodrazor needs to be:
1) Distinguished from Wit's End, so that the player can immediately upon viewing it recognize that each fit separate niche's and should not see one as overriding the other's right to an inventory slot forever.
2) Re-designed to FEEL like a SHREDDING item. Buying this item has to make players WANT to jump ontop of health-stackers to get their visceral feedback from it, and actually get back meaningful, visible reinforcement for doing so.
3) After points 1&2 are done, it needs to be re-introduced to the community, to try to wash away the negative connotations/stigma that pervade the word "Bloodrazor" and open players up to experimentation again.
4) A task this grand likely requires the vast powers of Xypherous. To garner his attention, I suggest you set up a small candle-lit shrine outside of his office and burn offerings of papers written by PhD's. Lyte & Davin probably have a few somewhere...

Entropy is an amazing item, and it's a shame it's not available on SR.

Kitae's is the same kind of trap Bloodrazor is, except it deals even less damage, and set's the user back by less gold.

Sorry for another post so soon, but there is the thought that Entropy is kind of at cross purposes. Generally, champions who want Phage are tanky bruisers that have enough sustained damage that, once they proc the slow, can eventually kill anyone except for stronger bruisers. That kind of champion usually builds Triforce as their main (or more likely, only) damage item and then defensive stats afterwards.

Entropy's niche basically seems to be champions who scale heavily with AD, but who also benefit greatly from an on-hit slow. Because most heavy-AD scaling champs (Riven, Talon, Zed, and even Lee Sin) are very burst-oriented and quite mobile, the slow is not exceptionally useful for them.

I honestly never make them...

Entropy is worth remaking into a Pickaxe instead of BFSword item. I'ts just too expensive right now, but it fills a niche on low cc sticky tanky jungle champs like Warwick and Olaf.

Kitae's in a better place than MBR, but it's still overpriced for what it does.

Hi Nome!

You pay a ton of gold for the active on Entropy - you're paying 600 gold for 7 ad, 50 health, and the active. The thing is, since phage already has a chance to apply an item slow of the exact same magnitude, the active is often completely wasted beyond a few hundred true damage (at best), which isn't much by the time you're buying, or can even afford, Entropy.

You could just make the item cheaper, but I think it would be compelling to just buff the active to be a more dramatic effect. For instance, when you pop ghostblade, it is a pretty significant moment and you feel pretty badass for a while. When you pop Entropy, you apply the slow that you had a chance to apply anyway.

There are a bunch of ways you could go with the active, and I'm sure the professional game designers can think of better versions than I can. The first thing that pop into my mind is to make the active a targeted ability with a Wither-like effect (it is called Entropy, after all) that progressively slows movement speed down to a crawl.

Entropy is nice, though a bit expensive to get. I'm not sure i agree with what other people are suggesting for it though, reduce the ad on it and it becomes overly similar to FM. Side note, if that active works with incoming runaan's hurricane, and from what i understand it does, might be a rather nice combo.

I would just remove kitae though, the basic premise is bad.