Stats wise, health scaling and regen are way too low, damage is a bit high (150 base AD at level 18. Ow.), attack speed and magic resist are all way too high. The highest base AS at the moment is just under 0.7, and most people don't reach an base AS of 0.9 until, like, 14th level. MR always scales as either +1.25, +0.75, or 0 (Depending on whether the champ is ranged or not), and 25 base MR is scary good.
Doesn't stack with itself but stacks 6 times? Your passive is confusing as hell, dawg. I don't think you meant to say base Attack Damage, because base attack damage is the attack damage he has from his level and nothing else. Any bonus would obviously not be added to that. 30% bonus base AD doesn't scale well into late game, but gives him a pretty potent early game.
After looking through his whole kit, I'm imagining his Ult basically makes his skills behave like Lee Sin's. An interesting idea, but a bit difficult to manage due to his ult's short initial duration.
90 (+45 total AD) damage at rank one is fair for such an ability, though scalings usually don't change from rank. In addition, most things that don't proc on-hit effects don't scale on total AD, only bonus, and it's usually a bit higher. I'd change it to 60% bonus AD on the first pass through, and 30% bonus AD on the return. Possessed variant is interesting, but again, just set it to a single bonus AD scaling.
AP scaling on this guy seems off, and again, scaling doesn't increase with rank. If this is a targeted dash, the base damage is way, way too low, and even if it's a skillshot pass-through dash that's practically nothing at max rank. Possessed variant isn't much to write home about, but it seems functional enough, so long as you raise the damage and change the AP scaling to AD.
Curious if the bonus damage is Lucien's or the target's current health. If it's Lucien's, that seems really awkward, as it gets progressively weaker as he does (Contrasted to gaining in strength as he looses health, which is both entertaining and offers an element of surprise.) An AoE heal on him just seems...off to me. I'd switch it to merely granting him a buff that provides a lesser version of the on-hit effects on all hits for a few seconds.
Ult is kinda awkward. It's a transforming mechanic, which is neat, but is does hella changes to his kit. Scaling per rank is off: All scaling per rank is always linear. 700 bonus health is quite a lot at max rank, though I suppose it's to compensate for his abysmal base health. You cannot add to base attack damage: That is literally its definition. It is the champion's attack damage before any modifications. If you want his passive to synergize with his ult, make his passive increase his total attack damage (which, again, obviously won't stack with itself.)
The big problem I see with him is that as he levels up, he basically 100% requires his ult to do much of anything. His scalings on a lot of things are really bad, but his Ult compensates for all of them. I'd change that up a bit. Make all of his scalings reasonable and then make his ult reasonable, and make his ult more reliable. 90 second cooldown on an ability so crucial to his functionality is a bad idea. Either give it a shorter cooldown, or make it a toggle with some sort of cost. A fury meter would go well here, utilizing it kinda like Shyvana.