Off the top of my head.
True final boss - Kirby Star Allies - If not the best, damn near close to being the best fight of my life, an spectacle, a challenge and a culmination of over 20 years of the deepest lore.
Bowser final fight - Super Mario 3D World
Tiki Totem - The Messenger
Zu Pharg - Xenoblade Chronicles X
Bashmaster the Unbreakable - Donkey Kong Country Tropical Freeze
Final boss - Fire Emblem Fates Conquest - I hate that boy, but god damn he gave me one of the best fights in Fire Emblem, an archer of all things.
Final boss - Pikmin 3
Urizen 3 - Devil May Cry 5 - Game should have ended here.
Dragorren - Little Town Hero
Pacifist ending fight - Undertale
Feel bad leaving out a lot of other awesome fights, but this will do.