Duskblade of Draktharr

Given the context when they introduced the item, they wanted an item that is on power with Infinity Edge and Rabadon's Deathcap, but for assassins. I think it's fair to say that they completely missed. Rabadon's Deathcap has a passive that scales with any other purchase made containing ability power. It strengthens your other items. Infinity Edge has a passive that scales with any other purchase made containing Crit Chance. It strengthens your other items. Duskblade of Draktharr has a passive that doesn't even work with other items, but instead works with a playstyle. And that is where they went wrong.

So what should the passive for the item actually be in order to fit the theme of assassin and to synergize with other items you would build as an assassin?

First let's look at what assassins build: AD, CDR, Armor Pen, and Movement Speed.

Now let's think about the role an assassin has: find weak spots and gain a kill (or get a "pick" on an isolated target) then move on to the next target. Assassins do not engage (which is why Rengar got so many nerfs), they instead time their attacks for maximum effectiveness.

This means the passive should interact with other items you build and should help you do your job as an assassin (clean up duty).

A few simple ideas are:

Essentially copying the Rabadon's Deathcap passive but scaling it with AD instead of AP. However this could be abused by ADC players such as Jhin. It's not a very effective solution overall.

Gain armor penetration that scales with your bonus AD. This helps against tanks but Lord Dominik's Regard and Black Cleaver, and the few +10 or +20 armor pen items seem to be balanced enough to not erase tanks and to help in dealing with tanks. Again, not a very good solution.

So that leaves CDR (not that big of a problem because items like Ghostblade, boots of lucidity, Black Cleaver, and blue runes before the game starts already helps you reach the cap, or come close to the cap already). And again, the Youmuu's Ghostblade active gives movement speed on a short cooldown, to help with getting to the right spots already.

So what is there to create synergy? What is left? Could there be a way to raise the cooldown reduction cap to 60% and make your cooldown reduction 50% more effective so that building 40% would equal 60%? That way assassins can burst more often? Is that healthy for the game?

Or can you just do this:

On Kill or Assist, permanently gain +1% bonus AD and Armor Pen. This way ADC can't abuse the item, since they have more important items to build FIRST. It's essentially a Deathcap that you want to build as first item. Or a Mejais that doesn't punish you when you die (but also isn't super cheap). You COULD build this on ADC but after you get Lifesteal item, I.E., attack speed/crit item, armor pen item. So you would have to replace Mercurial Scimitar or another defensive item and just go full offensive. But then you die easy to assassins. ;) And you don't get the bonus unless you get kills, which ADC has to focus less on and focus more on survival.

You could also focus on utility, but utility doesn't synergize with other items purchased. My first initial idea was an on-kill buff of stealth (disengage mechanic almost), which would be cool on another item but not an item that is looking to be on the level of Infinity Edge and Rabadon's Deathcap.

In fact, the current iteration of Duskblade wouldn't be so bad if the cooldown was instead 80 seconds. However, this change wouldn't give an item that they were looking for. It would just give an item that is more of a utility thing, like Phantom Dancer or Randuin's Omen, and not an item that increases the power of a full build assassin.