Lane harass and sustained teamfight damage.
Empowered abilities and resource manipulation
Hitting an enemy champion with 3 attacks or separate abilities grants a burst of MS.
Gain cooldown reduction and max cooldown reduction on your ultimate. This is increased further each time you use your ultimate, up to a maximum.
Gain 3% extra MS. Gain extra AP or AD, based on your bonus MS, Adaptive.
Your first ability hit every 20s burns champions.
+20 Ability Power or +12 Attack Damage, Adaptive
Gain a free stopwatch. Stopwatch has a one time use Stasis active.
+5% Max CDR
+5% Summoner Spell CDR
+5% Item CDR
Phase Rush on Swain massively empowers your ability to stick to your opponent while casting your ult as well as being able to stay in range for follow-up [Q] damage.
Swain's [R] has a rather long cooldown but the survivability it provides can grant you the edge in a skirmish the more you have it up, the better.
The bonus Movement Speed from Celerity is pivotal in re-positioning for landing a clutch [E] root and maneuvering with your [R] active in teamfights.
Scorch is an incredibly strong early laning rune for pressure and harassment. Look to proc the bonus damage as often as possible with either [Q] or [E].
Zhonya's and the stasis are a key part in taking over teamfights as Swain thanks to the ability to keep your [R] active and healing you throughout.
Cosmic Insight is an all-around fantastic rune choice for any champion as the extra bit of CDR helps you pump out more damage and stay safe with increased Summoner CDR.