|“||When a big enemy is defeated, eat him!”|
|— Intro description • Kirby's Adventure|
When a mid-boss is defeated they typically lie on the ground KO'ed for a few seconds before exploding. It is only during this time that Kirby can use his inhale on them to receive their Copy Ability as normally they are strong enough to resist his suction.
Most mid-bosses, with the exception being the Meta-Knights, are able to resist Kirby's inhale and have a health meter that must be depleted before they are defeated. They also have at least one attack that can be inhaled and spit back at them (this is the only way to beat them without a Copy Ability).
In some games, Mid-Boss Towers can be accessed, where many mid-bosses are faced consecutively.
Copy Abilities from mid-bosses
When a mid-boss is defeated, it normally lies on the ground KO'ed for a few seconds before exploding. (except for Sphere Doomers, Kracko Jr., Lololo, Super Bonkers, DX mid-bosses (Dededetour and Meta Knightmare Returns only), mid-bosses in Kirby 64: The Crystal Shards, Kirby's Epic Yarn, and Kirby Mass Attack). During this time, Kirby can inhale them and gain their ability. Nearly all mid-bosses have Copy Abilities and some Copy Abilities can only be collected from mid-bosses (e.g. Hammer, Suplex, and Ghost ability).
Mid-boss is a shortening of "middle-rank boss," referring to how the enemy isn't quite the rank of a normal boss, but cannot be exploited like a regular enemy. The "mid" in its name could also be interpreted in that the mid-boss generally appears in the middle of stages/levels instead of being at the end, where a normal boss would usually be.
|“||Some of the enemies are just too nasty for me to swallow. See if you can find other ways to beat these guys!
A medium-rank boss can't be swallowed up.”
|— There are Some Tough Guys Out There That Even I Can't Swallow! • Kirby's Dream Land Instruction Booklet|