Expanding on the previous post, let's talk about entire potential kits; I feel this'd work better than looking at individual potential abilities.

Disruptive AP Caster

Kit designed to lane purely on outplays. Shuts down key targets in team fights. Rewards success and punishes failure harshly on both sides.

  • Squishy, ranged APC with support potential.
  • Passive: Borrowed Time: Decreases the cooldown of your spells by 1 second whenever a nearby foe uses a spell, but increases the cooldown of your other spells (if they are already on cooldown) by one second whenever you use a spell. Gain a small amount of mana whenever your cooldowns are reduced by this passive.
  • Q (Active): Backfire: Foe-targeted debuff. Deals relatively small damage and applies a debuff to target foe for a very short duration; if they attempt to use a spell during that duration, it fails, that foe takes additional damage, and that spell goes on a short cooldown.
    • Instant. High-ish cost, cooldown to match average poke, and mid-range.
  • W (Active): Oblivion: Foe-targeted debuff. Applies a debuff to target foe for a few seconds; the next time that that foe casts a spell while debuffed, that spell's cooldown is multiplied and your spells' cooldowns are decreased proportionally.
    • Longish cast time. Quite expensive, longish cooldown, and longish range.
  • E (Active): Mana Burn: Large, ground-targeted debuff. Applies a debuff to targeted units, dealing mediocre damage over time that increases over the duration. You gain mana based on the damage dealt. If a champion is affected, you gain significantly more mana and they lose a similar amount; however, the effect ends if they use a spell. Quite expensive, but pays for itself and then some if used in the right circumstances.
    • Longish cast time. Cooldown and range to match average poke.
  • R (Active): Panic: Large, ground-targeted debuff. Applies a debuff for a few seconds to all foes affected; whenever one of those foes uses a spell, deals a small amount of damage to other nearby foes (not the caster) and silences them for a short duration. Deals the same damage on autoattacks, but does not apply silence.
    • Short cast time. Expensive, but not prohibitively so, with a longish cooldown and range.

High-skillcap AP Melee Mage

Get ready for some heavy reading, because this concept isn't "easy". In the interest of speeding the process along, I'll put the whole thing in easy terms up-front:

Q drops an arrow on the ground after a very small delay (like a Syndra Q); stepping on that arrow shoots a unit in the direction that it's pointing, destroying that arrow in the process. Anyone can step on arrows, for or ally, champion or minion, and the caster can decide where the arrows point on when they cast them. If things hit other things due to the arrow launch, damage happens, but not to allies; it can also be a wallbang.

W passively gives on-hit bonus damage every 3rd hit (like Vayne, Vi, or kind of Diana), except that last hit is also a knockback (instantly drops a Q arrow directly under the foe; no delay). W also has an active component, which can be cast on self or an ally (like Nami's W), which gives bonus attack speed and 3 empowered AAs, with each charged AA dealing bonus magic damage. If all three attacks hit the same thing, it deals even more magic damage and drops its Q arrow under the target, just like the passive. The passive is lost while on CD.

E passively gives this champ a shield when they're launched by a Q arrow. Whenever this champ is launched by anything, though (like Q, or a Lee kick, or Flay, or Moonfall), they can use E actively to stop that launch immediately and gain a charge; they can use the charges to activate a dash, which also gives a shield (kind of like Riven's Valor). As long as the shield is up, it helps to stick to runners or to escape pursuers, but not much.

R makes the arrows from Q (and W, since it's a Q arrow) shoot in the direction they're pointing; they do damage on impact, and also have all the same knockback rules as Q, so they can potentially do even more damage by making stuff hit other stuff. When the arrows are shooting, though, they can't affect allies.

That's the simple version; here's the more detailed version:

  • Relatively beefy (for an AP Caster) largely-AA-based melee mage with support potential.
  • Passive:
  • Q (Active): Vector Arrow: Ground-targeted vector "skillshot". Places a mark at the vector's initial location that lasts for a few seconds, pointing visibly in the vector's direction; when stepped on the unit that activated it will be instantly accelerated in the direction of the vector, with their speed decaying over the duration of the launch. The mark is consumed after triggering once.
    • On ally/self trigger: you or that ally deals AP-based magic damage on collision with foes; if you or an ally passes over a mark while being launched in its opposite direction, that mark shatters, causing you to lose a charge and stopping you/that ally's movement immediately.
    • On foe trigger: foes stepping on the mark are launched in the direction of the vector, taking damage on collision with, dealing less damage to, and knocking aside other foes they strike; on collision with terrain, that foe takes damage and is stunned for a short duration; if a foe passes over a mark while being launched in its opposite direction, that mark shatters, instead, dealing significant AP-based damage and rooting the foe that triggered it.
    • If a vector direction is not definitively specified on cast, it "intelligently" orients itself (ala Draven axes); I'll even include the recommended behavior:
      • Consider four "zones" around and between the ally and foe nearest the target location: the space closest to the ally, both toward and away from the foe, and the space closest to the foe, both toward and away from the ally. We'll call them "ally in" (1), "ally out" (2), "foe in" (3), and "foe out" (4), respectively.
      • In the most complicated case, both the ally and foe are attacking each other; in this case, the vector mark should point directly toward the foe if in zone 1 (ally wants to engage), away from the foe if in zone 2 (ally wants to disengage), away from the ally if in zone 3 (foe wants to engage), and directly toward the ally if in zone 4 (foe wants to disengage).
      • If the ally is chasing/attacking a fleeing foe, the mark should point directly toward the foe if in zone 1 or 3 (ally wants to engage), directly toward the ally if in zone 4 (foe wants to disengage); it should point directly away from the foe if in zone 2 (ally has changed their mind and now wants to disengage).
      • If the ally is fleeing a chasing/attacking foe, the mark should point directly away from the ally if if zone 1 or 3 (foe wants to engage), directly away from the foe if in zone 2 (ally wants to disengage); it should point directly toward the ally if in zone 4 (foe has changed their mind and now wants to disengage).
      • If there are no visible foes nearby, non-targeted should point directly away from the nearest ally if placed in front of them (speeds them in a direction) and directly toward them if placed behind them (helps allies to group).
      • There may be additional cases that I haven't considered, but I think that the fact that you can, in fact, manually orient the vectors ought to solve most problems. I know what you're thinking: "But wait, then why have auto-targeting to begin with?": simple answer is "because you have other things to do". You're a melee mage; when you're going in with W and want to place a mark behind your foe so you can proc the damage/CC with your last W charge, you don't have time to be lining up arrows; you're meleeing. It's a QOL thing.
    • No cast time, but with a short, visible delay before the mark is active. Uses a charge system, with a few able to be stored at once and a relatively low cooldown between charges; low mana cost, longish range.
  • W (Passive): Vector Blade: After three consecutive autoattacks on the same foe, deal bonus AP-based damage and create a Q mark at that foe's location, pointing directly away from you; the mark triggers immediately unless that foe was killed by your autoattack. Passive is lost while on cooldown.
  • W (Active): Vector Blade: Ally-targeted buff. On cast, instantly place a Q vector at target ally's location, pointing in the direction they are currently facing. Empowers target ally's weapon for a few seconds, granting them bonus attack speed and causing their attacks to deal bonus magic damage based on your AP; lasts for 3 hits. If all three hits strike the same target, the final strike deals additional magic damage and creates a Q vector at the location of the struck foe, pointing directly away from the targeted ally; the mark triggers immediately unless that foe was killed by your ally's autoattack.
    • Instant. Relatively expensive, medium-long cooldown.
  • E (Passive): Momentum Shield: While dashing from activating a Q mark (including from W), gain a small absorption shield based on your AP that decays to nothing over time, ending completely one second after the dash ends.
  • E (Active 1): Halt Inertia: If you were in the middle of any forced movement (including from a Q mark or Dark Passage), end that movement immediately and gain one charge for this ability, up to 3 max. The passive shield fully dissipates over the next second, regardless of how much of it remained on activation.
    • Instant activation. Moderate-ish cost; short cooldown. Notably, cannot be used while stunned, so precludes stopping Thresh and Blitz pulls (unless you have Cleanse or QSS, but then that's still clutch as fuck; I can't even be mad at that).
  • E (Active 2): Renew Inertia: Consume one charge to gain a substantial absorption shield for a few seconds and dash a short distance toward the cursor. While this shield persists, your attacks draw you and your target together a short distance and attacks against you push you and your attacker apart a short distance.
    • Instant activation, relatively fast dash. No cost, no cooldown. Pull/push distance is very small; the combined effect should be less beneficial than Frozen Mallet for stick/peel. Of note, E can't be used to stop an E, since it's not a forced action.
  • R (Active): Vector Storm: Non-targeted spell. Causes all currently-placed marks from Q to change into collision linear skillshots that fire rapidly in the direction they are pointing, dealing significant damage to and knocking foes in their direction, according to the rules of Q, exactly as if they'd stepped on the marks. Marks do not affect allies while in this state.
    • No cast time, but with a visible delay before actually activating. Medium-short cooldown, medium-low mana cost.

High-skillcap AD Assassin

  • Squishy melee AD assassin/carry.
  • Passive:
  • Q (Active): Knives from the Shadows: Narrow cone/wide line of linear collision skillshots. Deals moderate AD-based damage; deals bonus damage to and roots foes that are not visible. Can critically strike.
    • Cast time scales with your attack speed. Relatively spammable, with low mana cost and cooldown. Decent range.
  • W (Toggle): One With Shadow: Self-buff. Enter stealth, but lose vision of enemy units (ala Paranoia) outside of the immediate area. Using an ability temporarily breaks stealth (does not restore your own vision), but you gain a significant burst of movement speed whenever you enter stealth. While toggled on, Q's cost and cooldown are reduced by a significant amount, but its root effect is replaced with a slow.
    • Costs a bit of mana on activation and also a small amount per second.
  • E (Active): Blade in the Dark: Linear passthrough ground-targeted dash. Dash to target location, dealing strong damage to and stunning all foes you pass through. The damage, range, and stun duration of this ability are increased based on how long you were stealthed for before using it, up to a cap. If using this ability while stealthed, you are revealed for the cast time, but your stealth is not truly broken until the dash completes, at which point you gain bonus attack speed for a short duration.
    • Short but noteworthy cast time; medium-long base range; relatively expensive with a moderate cooldown.
  • R (Active): The Stuff of Nightmares: Self-centered area effect. Remove nearby allies' and foes' vision of units outside the immediate area for a short duration. During this time, the presence of any champions in the affected area is revealed to you (you do not gain true vision of them; they are only marked to say "a champion is here"), and using an ability only reveals you to any foes struck by that ability. You gain massively increased movement and attack speed for the duration.
    • Moderate but not prohibitive cost; longish cooldown.