Looking to develop a "Support Assassin" Champion, and need help brainstorming

"What do you mean by 'Support Assassin'?"

Essentially, it would be a Champion who, like a Support, provides benefits to teammates and can't easily kill enemies on their own, but like an Assassin, can cause an enemy squishy to die VERY quickly. How does this work? This "S-Assassin" (for short) would place certain debuffs on a target, making it extremely vulnerable and allowing allies to quickly snipe it. This would not just be stuff like crowd control, but things that cause the target to take extra damage and the like, while also isolating the target so its allies cannot save it in time.

"Why would we want this?"

Most compositions today are better when you have AOE rather than single-target annihilation. Supports generally lean toward the AOE side of things, with a few exceptions (i.e. Braum). A Support who lets his/her teammates obliterate a target in less than a second would be cool.

"What sorts of skills would this Champion have?"

That's something I'm still working on, but I have at least two skills for the kit that I like. They are below, but remember that they are prototypes; they will be subject to change.

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Archaic Curse

Deal modest magic damage to target enemy and mark it for a few seconds. Basic attacks from you or allied Champions onto a marked target deal bonus magic damage. The bonus damage proc is X% weaker than the last for each consecutive hit. EX. 100 -> 80 -> 64 -> 51.6 -> etc. (if damage were to decay at a 20% rate)

Implosion (this would be an ultimate)

Fires a projectile that deals magic damage to target enemy Champion, stuns it for 1.25/1.5/1.75 seconds, and knocks away all nearby enemies, dealing magic damage to them as well. The projectile can be intercepted by other Champions.

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I'm hoping to make such a kit for a Harpy Champion. I figure Mount Targon needs more in its roster.

Anyone wanna help? Post up your ideas.