Instant effect
Increase Buff Duration
Increase Buff Duration is the game's own name for this effect on the battle screen. The game gives no separate description for it.
Champions with it
39 champions have a skill with a Increase Buff Duration effect, according to the effect lines in the game data. This lists who has it and on which skill, not how strong it is or how often it happens: values and chances are on each champion's page.
Alatreon Blademaster Foresight Slash (all allies)
Anchorite Prayer of Prowess (all allies)
Androc the Glorious Radiant Claw (all allies)
Andryssia Pointed Justice (all allies)
Arashi the Riptide Nautical Assassin (this champion)
Arbais the Stonethorn Verdant Rebirth (all allies)
Bambus Fourleaf Grovetender (all allies)
Bladechorister Caldor Orchestra of War (all allies)
Bowf the Rancid Spearstench (all allies)
Brewguard Jeroboam Last Orders (all allies)
Corvis the Corruptor Medical Miracle (all allies)
Craklin the Blackened Blisterblast (all allies)
Demytha Light of the Deep (all allies)
Diamant Coppercoin Charitable Donation (all allies)
Duedan the Runic Protector Effigy (all allies)
Dune Lord Greggor Earthcleave (all allies)
Flesh-Tearer Warleader (all allies)
Giath the Truthshield Truth Beheld (all allies)
Godseeker Aniri Quest For Meaning (all allies)
Graazur Irongut Healing Bombardment (all allies)
Hellborn Sprite Transmuter (all allies)
Highmother Maud Anointed Phalanx (all allies)
Hope Hearten (all allies)
Krisk the Ageless Centuried Vigor (all allies)
Lady Mikage Silkensnare (all allies)
Lanakis the Chosen Companions of Fate
Lightward Siendra Resplendent Burst
Mad Hatter A Whiff of Madness (all allies)
Malkith Bloodflock Hemobomb (all allies)
Oella Hand of Spring (all allies)
Quargan the Crowned Nature's Cycle
Sandlashed Survivor Endless Sands (all allies)
Senna Amberheart Healing Glow [P]
Shemnath Caryatid's Curse
Taras the Fierce Constant Pressure (all allies)
Valerie Energizing Presence (all allies)
Vault Keeper Wixwell Tempest of Knowledge (all allies)
Wysteri Vineguard Burrowbolt (this champion)
Wythir the Crowned Feel No Pain (all allies)
Taken from the game data and not tested in battle here. See Data quality.