Master Kohga is the last enemy in Yiga Clan Hideout. He's more of a gag and the fight is one of the easiest in the game. You will just need regular arrows.
Initially, the enemy will summon bombs that will hover over him for some time. Just shoot him, and he will lose focus, causing the bombs to fall on him. He'll be stunned: approach, and attack with melee weapons. After this happens a couple of times, the enemy will adjust the strategy - hover over the middle of the arena and summon two bombs! Wait until one of the revolving bombs is above him and shoot him again.
Finally, the enemy will summon an even bigger bomb. Use the magnet to bring it above him and drop it: this will allow you to definitely win this fight.