For reference, my version of Swain-
Passive-Corvid Swarm: Swain keeps a murder of 5 Ravens around him. Every time he auto-attacks, a Raven shortly follows to attack his target, dealing X damage(Scaling each level with an AP scaling) and inflicting Torment on the target, increasing damage by X% from his other attacks for 2.5 seconds. Swain gains one Raven every X seconds.
Q-Swain sends out a swarm of Ravens to attack a target area for 3 seconds. Deals 100% bonus damage to minions, deals AoE damage to minions. If an enemy champion is in the area of the swarm, the Ravens will converge on them. Swain will also launch his Ravens from his passive for a flat X damage towards the champion, and if the enemy champion had a Raven on them already, it'll refresh the duration of the Torment.
(I'll focus on Q for this post)
I like Swain being Oppressive
His Q is extremely oppressive combined with his passive. I also feel on review that Torment does seem a bit excessive for his passive(As it already provides a damage boost to his auto attacks, along with boosts to his Q/W which feed off it.)
So having Ravens as a Resource Reserve is #1. His Q is oppressive in the way that it can deny an opponent farm in lane, and consuming his passive ravens for a damage boost can be extremely OP. On the flipside I was thinking that because it does consume all the ravens upon hitting an opponent, it's the trade off to Swain using his Ravens to farm, and decreasing his overall power since it denies the boosts to damage on his W/E/Auto attack. And provided the Counterplay that an opponent could avoid stepping within the Murder of Ravens..
So how about add a slight delay to his Q. Marks a place on the ground where the Ravens will flock to. Gives an opponent a chance to get out of the way, whilst retaining the use to farm with it, as well as denying an opponent either a path to attack you, or deny them the ability to farm without taking damage. Since it's Swains main nuke, putting a cooldown of about 10 seconds is decent. If an opponent picks up the Q by walking over it(IE you were using it to farm, and they walk over it), then whatever time remains determines the damage they take. Let's say at rank 5, it stays on the ground for 3 seconds, doing 300 damage in total(600 to minions). If an opponent walks 2 seconds in, they'll take only 100 damage(+whichever ravens converge from Swains passive).
Basically, it's a skill with tradeoffs-Slight delay before it hits, the opponent can see where it is, moderate cooldown, and it drains your resource of Ravens if it hits an opponent. There is also no CC to it-in my version of Swain, his only CC will be his Nevermove.
As for an ultimate..I was thinking about what you said. That Ravens need to be a part about his ultimate. So I surmised an ultimate where the whole battlefield would become engulfed with Ravens. That is, they would be perched on the fixtures of summoners rift-On stones, in the bushes, around the pits, on trees.
R-Pact with Corvus: Hundreds of Ravens converge among the battlefield for 1 minute. Whenever Swain hits an opponent with an attack or ability within 500 radius of any Ravens, a nearby Raven will converge on his target providing extra damage, until the Ravens in that area are exhausted. You can press R again to cause all the remaining Ravens within your radius to swarm where you clicked. Can be activated again 2/3/4 times. Cooldown starts after ability ends(Similar to Yorick). 150 CD for first rank.
So basically, this is enforcing the fantasy of Swain being a master of magic and Ravens-Ravens are his familiars, and maybe he made a pact with something greater to gain mastery over them. So this ultimate is a map wide ultimate(It provides no vision however). And only in the areas where Swain is, will the ultimate work. It's very location based-That is, once you exhaust an area of Ravens, then you'd have to move to another in order to keep using it to the most effect. The counterplay being that if you're away from Swain, or if you force him to fight in one spot too long, he loses out on his ultimates power. The flipside being that skirmishing/trying to run away becomes dangerous because you'll only run into more Ravens.
Having an activation to use up all the Ravens near Swain is also a trade off-Swain can use his ultimate again to make Ravens around him fly ahead of him(Think Xerath's Q) before dispersing. However, this does a flat amount of damage, a lesser amount than if Swain individually used up each Raven around him, and he can only do it a limited number of times during his ultimates activation.
And there you go, no more transforming and no more healing. Swain becomes a Nuker who has to think about how he'll use his abilities.