I like Mephisto's skillshot ult so here's a pitch

i have no theme or pre-existing IP here, i just like trying to hit people with Mephisto’s root ult that self-roots you while you channel it, is very fast and has a tiny radius. But bc of how high CD/high reward the ult and how it ends the game when you land a shot, I don’t get to toy around with it like you do Kaelthas’s Q. So here’s a pitch for a hero that is basically “what if Kaelthas but his Q was Mephisto’s R skillshot, without the high CD & proportional reward?”. That’s it, you can stop reading here

So, a mage character, IDC who/where/what/when, themed around lightning – tho it doesnt matter.

Q; channels in place for 0.8 seconds then throws a lightning bolt projectile in the target direction, travels 14 range (40% farther than flamestrike, a hair shorter than durance & longer than shield glare) with a radius of 0.5 (double durance, one quarter the size of flamestrike) at a speed of 22 (exactly the same as durance but twice as easy to land bc the projectile is fatter), damaging the first enemy it hits. It has no baseline AOE component, target is slowed by 30% decreasing over 1 second

W; creates a circle on the ground with a radius of 1 (half of a flamestrike) within a range of 5 (hair less than living bomb), after a 0.75 seconds everyone in it gets shocked, damaging enemies and giving allies movement speed. If it damages an enemy hero this character gains a flat shield (have to take talents to get more value from hitting more than 1 enemy) & movement speed. Doesn’t do good damage, this isn’t an AOE hero

E; Mirror Shield. Creates a clone of yourself (that is visibly not the player, this isn’t another Nova/Samuro trick spell) in target direction at a range of 0 (pushes enemy or teammates to make room for it, so can be used to disjoint enemies away from you like Blademaster Windwalk in WC3).
Clone has 1 HP, does 25%(or less damage), mirrors your Q casts & move/attack orders – he sticks to you & does what you do but can’t bodyblock you (if you walk into a wall & he’s in between you and the wall you push him aside without slowing down).
The one thing the clone does that you don’t; it has an aura that gives you 25 spell armor, making you take less spell damage while it is alive (& ur next to it, if u get hooked it doesnt help u). If you get farther than melee range away from it it leashes to you, mounting dispels it, it lasts 8 seconds, has 16 second cooldown, when it takes damage it self-dies so hitting it counts as dealing 1 hero damage for your enemy but not a kill.

R; Idk lol the hero pitch is the Q, do you care? Actually in case you do; R1: This hero channels for 3 seconds & rises into the air, everyone on the map gets a lightning storm GFX (Similar to stitches swallow) that warns them this is coming. When the channel is over the hero can instantly throw a burst of 5 global-range Q’s in a target direction, each one traveling slower than the last. Getting hit by one from farther than sight range reduces your movespeed by 40% for 1 second stacking (so getting hit by one makes it more likely to get hit by the rest).
At lvl 20, hitting someone with this spawns a Storm Djinn on them for 5 seconds that is invulnerable, targets the enemy hero hit with a melee range tassadar beam, immolates with static electricity for constant AOE damage (chunking a whole team with this does 5x as much AOE dps per player if the djinns are stacked) and all damage they deal grant this hero shield.
R2: A second, independent cast of your D (see below). That’s it! Because your D has a special mana-draining mechanic, and your 1 is a special mechanic to get mana back, it wouldn’t be broken or (probably) underpowered to just give your character a second D but would instead intensify interaction with those two mechanics, especially since your D both makes your spells combo and also makes your spells better if you don’t need to combo, so there’s design tension there.
At lvl 20, the R D can store up to a second charge with a 1 second cooldown between uses, but using it while it has 1 charge resets it to 0 (giving you a rotation (you can use your D freely as you did before but you want to hold your R until it’s double-charged for a potential triple-tap of empowered spells); hitting an enemy with an auto attack within 1.5 seconds of damaging them with an empowered spell (or just casting the spell in the case of the clone) reduces their armor by 5 for 3 seconds, stacking, you damaging them resets its duration; you can use this to thunder-crack someone’s armor to make them killable but the spell you can do this with that does the most damage is also your hardest-to-land skillshot, and your target will know you’re out for them making it an extra challenge for you both.

1; Quest; Deal damage to enemy heroes. Reward: Periapt of Power; activate to double max mana for 5 seconds, upon reaching half mana (IE ur non-periapt max) this effect ends early. Also increases spell power by 7% and reduces armor by 15% for 5 seconds (doesn’t end early). Every second of a regen globe decreases the cooldown of this by 5 seconds, drinking from a fountain resets this cooldown. ((this activatable doubles the mana gained from globes and fountain which go off max mana, but makes you easier to kill while ur doing it)).
Mythic Quest; Get 5 takedown while the Periapt is active without dying. Reward: Dying while the Periapt is active or for 5 seconds after it expires makes you an unkillable ghost for 1.5 seconds and then returns you to life at 1 HP. While unkillable it replaces your basic abilities with 3 Bolts of the Storm; each one extends this to 1.5 second, the first has no special effect & is a freebie, the second increases the move speed of allies and decreases the movespeed of enemies, the third damages enemies and gives allies a shield. The final bolt you cast has its effect on others doubled and grants you that benefit too; if the no-effect bolt is your last it has doubled range (but leaves you at 1 hp), if the speed bolt is your last it gives you movespeed (but leaves you at 1 hp), if the damage bolt is your last & you drop onto a teamfight you land with 1 HP but gain a permanent shield for the value of all damage dealt to enemy heroes and shields given to allies.
Since the Mythic Quest is to get kills without dying, cheating death with the Pariapt breaks it, and you have to do the quest over again.

D; Consumes 20% of your current mana and empowers your next-cast basic ability.
Empowered Q; now also pierces all enemies, doing minimal damage to enemies it passes through and dealing full damage to the last enemy it hits. Grants you double the shield and movement speed as your W grants, for 1 second, increased by 1 second for each enemy hero you hit.
Empowered W; explodes faster (0.5s) and slows all enemies hit by 45% for 1.5 seconds and doesn’t decay.
(Notice, your baseline Q slows enemies so ur W is easier to land but ur W doesn’t do much. You can Empower your W to slow enemies instead so you can hit them with your Q easier, but if you don’t need it/can call your shot an empowered Q does more to more enemies, and lets you snipe enemy squishy backliners, which tanks/frontliners can counter by pressuring this character to force them to throw an empowered W to save themselves)
Empowered E; the clone is spawned with bonus health (40%(your current mana +20%)* ), deals double damage and self-heals for all damage dealt
* (note the empowered clone gets bonus health for your current mana, not the mana you had after you pressed D; you can press D to empower your next spell, and then not cast a spell until later to regenerate mana over time, increasing the health it spawns with an effectively negating the mana cost of it entirely, assuming you can call your shots & don’t get ambushed

Talents, in no particular order;

your Q does more damage, each enemy an empowered Q passes thru increases damage to its final target

a second after your W damages enemies, they all damage eachother if within range of eachother (short range, like mephisto AOE attack radius). Each enemy hit by the secondary shock reduces the CD of your Q

clones have no duration, after being alive for 8 seconds they restore all mana they cost (including the 20% if you empowered it), after being alive for 16 seconds they can mount

being above 90~ish% mana increase spell power and mana costs by 40%. while below 40% mana, doubles the duration of regen globes

auto-attacking an enemy within 1 second of hitting them with your Q resets the cooldown of your Q at 60% reduced damage (reduces the damage of your Q by 60% for [insert CD here])

every time a clone attacks an enemy, this hero and all of their clones zap them with static electricity for a small amount of damage. every static discharge increases the damage dealt by future discharges by 1, stacking infinitely but resetting to 0 when this hero has no more clones left or dies.

all damage dealt by the player grants health to all clones (like an empowered clone self-heals but doubled/quadrupled since u double/quadruple damage as them, and multiplied by however many of them you have, and you don’t have to empower clones to give them survivability), all clone attack damage is increased by 50%.

each clone blinds the first enemy to attack it, increases spell shield gained from clones.

takedowns increase the duration of currently-active Periapt to 10 seconds and increase the damage increase and armor decrease by its base amount (14, 21, 28, 35/15, 30, 45, 50).

at the end of its path your Q turns into an un-talented Q with infinite range that does 50% less damage and 50% reduced damage to non-heroes. Every enemy hit by this reduces the cooldown of your Q by 2.

an activatable that makes you spawn a mirror shield clone in the direction of the nearest seen enemy (otherwise in front of you) every 8 seconds. Dealing damage resets its duration, and while it’s active it replaces your E with a Collapsar spell that consumes all of your clones for 20% max mana for each. If you have enough clones to go over max mana, consuming them does an Alarak-pull towards you on all enemies you can see and temporarily increases your max mana to however much mana you have until you go back under 100%.

a bolt of the storm that leaves behind an empowered clone that isn’t leashed to you, isn’t visibly a clone (unless revealed by something that can see invisible), follows your last command and then auto-attacks and Q’s at nearby enemies (but doesn’t track the Q at all). If it sees a friendly minion it a-moves up the lane like a minion. if you’ve taken the permanent clones talent this is a free catapult-spawning lane exit spell, if you’ve taken Q build you can use this to blink out of an enemy’s sight range and then Q them while they run up on your clone.

casting W while mounted gives it global range & teleports you to it if it hits an enemy. This would normally need to be a 20 talent or have an external cooldown, but since missing leaves you without a mount at a time when you want to be somewhere else, I think this is fine lol it’s hard and unlikely to miss (and it could be an un-talented version of the W that’s easier to dodge), but the punishment for missing is so bad