Blitzcrank vs Swain

Fire Rocket Grab (Q) from a brush or a side angle: it grabs the first enemy hit, so you need a line without minions.

After a successful grab, cast Power Fist (E) right away: your next auto knocks the target into the air and deals double damage.

Sometimes engage without a grab: rush in with Overdrive (W), knock your target into the air with Power Fist (E), and save Rocket Grab (Q) for when they Flash away.

Use Mana Barrier (passive) to bait: at low health you get a shield based on your mana, enough to make a kill look easy.

In teamfights, save Rocket Grab (Q) for their carry and wait for them out of vision: grabbing them before the fight starts often decides it.

Get out of the Nevermove (E) path as it comes back: it only roots on its return to Swain, then he can pull each rooted champion to him.

Leave the area as soon as Vision of Empire (W) appears: it strikes and slows 1.5 seconds later, and each champion hit gives him a Soul Fragment.

During Demonic Ascension (R), back off and hit from range if you can: he only drains nearby enemies, and his form ends when he stops draining.

If you have Grievous Wounds, apply it during Demonic Ascension (R): the drain heals him every second, and that healing keeps him alive.