Killian, Ink Duelist
Legendary Creature — Human Warlock
Lifelink
Menace (This creature can't be blocked except by two or more creatures.)
Spells you cast that target a creature cost 
less to cast.
"When your father is Dean Embrose, second best really isn't an option."
2/2
Illustrated by
Strixhaven: School of Mages#197UncommonEnglishLegality
Rulings
Apr 16, 2021
Killian, Ink Duelist can’t reduce the colored mana requirement of a spell’s mana cost.
Apr 16, 2021
Killian can reduce alternative costs. For example, if you choose to pay the 
alternative cost for Baleful Mastery while targeting a creature, that cost would be reduced to .
Apr 16, 2021
If a spell has additional costs, apply those increases before applying cost reductions.