Dark Meta Knight is the boss found in Radish Ruins. Due to the boss's high variance in RNG, the boss is usually fought early into the speedrun.
Sword
For most of the fight, you will want to use separated neutral swings, which are efficient since they are the fastest and most damaging attack available. In addition, you can also slide, which usually causes the boss to jump and thrust downwards. This is useful for preventing the boss from performing less favorable attack patterns. If you slide from a distance, and then perform a jumping spin attack right after hitting the boss, you can safely hit the boss while it down-thrusts.
Some attack patterns, such as the down-thrust, will drop stars. Upon inhaling, they give you Sword in case you lose the ability during the fight. You can try to shoot the star if the boss has low health, however this can greatly backfire if the boss parries the star bullet.