Okay, I just went to a lot of effort to make this, but I think you'd enjoy my idea.
Neo-Nao, The Astral Twins
HP: 435 (+29 per level) HP Regen: 5 (+1 per 5 seconds per level) MP: 240 (+31 per level) MP Regen: 4 (+1.5 per 5 seconds per level) AD: 56 (+2.6 per level) Movement Speed: 355 Attack Speed: .675 (+4% per level) Attack Range: 125 Armor: 26 (+2 per level) Magic Resist: 29 (+3 per level)
Passive: Neo-Nao each have separate healthbars. Neo gains 75% of max HP for his, and Nao gains 65%. Both gain 75% max MP. HP and MP regen apply to both of the twins at all times. Whenever one dies they both die, but this only counts as 1 kill. Cooldowns for abilities are champion specific.
Q: Neo-Nao throws the astral mirror in a target direction, acting as a 100 unit wide 20 unit thick passable wall to all units with an up to 200 unit cast range, and if Neo-Nao walks through it, they are changed into their Astral sibling. If a champion besides Neo-Nao walks the mirror they are dealt 6/7/8/9/10% missing health magic damage regardless of team. The wall lasts for 3 seconds, and this has a 20/18.5/17/15.5/14 second cooldown. This ability does not cost mana. This ability can be used while silenced.
(Neo) W: Neo dashes to an allied champion within 350 units, granting both of them 40/55/70/85/100 movement speed and purging any slows. This costs 40/45/50/55/60 mana and has a 6 second cooldown.
(Nao) W: Nao dashes to an enemy unit within 450 units, stealing 20/30/40/50/60 movement speed from them for 3.5 seconds. This costs 80/75/70/65/60 mana and has a 9/8/7/6/5 second cooldown. If this ability is used on an enemy again while still active, it refreshes the slow on the enemy but Nao stacks the movement speed up. Doing so also refunds 40% of the mana cost.
(Neo) E: Neo headbutts an enemy champion within 175 range, taking 10% of this abilities physical damage himself, but dealing 70/110/150/190/230 +80% Bonus AD +60% AP physical damage and stunning them for 1.25 seconds. Enemies hit in the last 8 seconds have a .5 second longer stun applied. 10/9/8/7/6 second cooldown. This ability costs 55/60/65/70/75 mana.
(Nao) E: Nao latches herself onto an enemy within 125 units with a wire. Unless they teleport, this wire persists. If the enemy moves, and Nao isn't moving, their movement speed is reduced by 80% but Nao is dragged along. If Nao is moving in the opposite direction, they are both effectively snared. Both players have dash ranges reduced by 60% while the wire is in place. Nao can cancel this ability by pressing E again. This ability has a 10 second cooldown after breaking, and costs 100/90/80/70/60 mana. While this is active Nao gains 30/40/50/60/70% attack speed while attacking the latched target, and auto attacks deal 10% AP on hit.
R: Neo-Nao place the mirror on the floor and pull their twin from it without entering themselves. After a 1.5 second channel to do so, for the next 15 seconds both siblings are out. Q loses it's cooldown, but instead just swaps between the twins. Only if the one you currently are dies does it count as a kill (Killing the other twin grants 15 gold). The second twin can be controlled using the R button (Think Mordekaiser). When the ability ends the twin you aren't is sucked into the mirror, regardless of current location, and this ability goes on cooldown. Additionally, whenever Neo-Nao dies all enemy champions involved gain a stack of Astral Curse, boosting Neo-Nao's damage to them by 5/10/15% per stack. Whenever Neo-Nao gets a kill (3) or assist (1) on marked champions a number of stacks are removed. This ability costs 50 mana from both of the twins, and has a 120/100/80 second cooldown.
Not much of an assassin, but I think this about fits what you wanted otherwise. Problem with making an assassin like Jayce or whatever is that one ability has to be taken up with their transformation. Because they are completely different champs, I also figured their passive needed to be taken up. Nao is a single target bruiser while Neo is intended more toward survival or repositioning.
Thank you for reading!
