Room Guarder

A Room Guarder is a type of mid-boss that was popularized in Kirby 64: The Crystal Shards. They generally consist of many regular enemies in a room, in which the room cannot be exited until they are all defeated.

Kirby's Adventure and Kirby: Nightmare in Dream Land
Room Guarders make their first appearance in Kirby's Adventure as the Meta-Knights. They are the only type of Room Guarder in the game, and appear in every level except Vegetable Valley and Rainbow Resort.

In Kirby's Adventure, the boss theme plays; in Kirby: Nightmare in Dream Land, the mid-boss music from Kirby 64: The Crystal Shards plays. The reason for the music change is likely because Kirby 64: The Crystal Shards was the first game to have its mid-bosses be exclusively Room Guarders.

Kirby Super Star and Kirby Super Star Ultra
Like in Kirby's Adventure, the Meta-Knights are the only Room Guarder mid-bosses in the game. They appear numerous times in the sub-game Revenge of Meta Knight, but have also appeared in Dyna Blade's Mallow Castle and The Great Cave Offensive's Old Tower. Usually only two are actively fighting in Dyna Blade and The Great Cave Offensive, while in Revenge of Meta Knight, usually three are actively fighting. The Meta-Knights are also occasionally just regular enemies, only occurring in Revenge of Meta Knight and in the fight against Galacta Knight (however, all three Meta-Knights summoned must be defeated in order to advance the fight, similarly to a Room Guarder).

Kirby 64: The Crystal Shards
All of the mid-bosses in this game (except for Waddle Dee/Waddle Doo, Adeleine, and King Dedede) are Room Guarders, however, most of them feature a large version of a regular enemy. Regular-sized enemies, usually of the same type as the large one, can be used as ammo if Kirby does not have a Copy Ability; they respawn after being defeated. Once the large enemy is defeated, the regular enemies are also defeated and do not respawn, and Kirby is allowed to exit the room. Some of them also drop a Crystal Shard for Kirby to collect. In the fourth stage of Neo Star, there is a Room Guarder that is simply a bunch of Drops falling from the ceiling. Stage 3 of Ripple Star also features Room Guarders that are various regular enemies without a large one in the room. This area serves as a mid-boss tower.

Kirby: Canvas Curse
All of the mid-bosses in this game are also Room Guarders, however, they have much less variety of enemies, although are generally more unique than those found in Kirby 64: The Crystal Shards. The Room Guarders consist of Spear Waddle Dees, explosive balloons, and bomb on parachutes. The latter two Room Guarders can only be defeated by tapping on them, whereas the Spear Waddle Dees can be defeated through traditional means.

Kirby and the Rainbow Curse
Being a successor to Kirby: Canvas Curse, this game also features Room Guarders. Special Blue Bronto Burts appear and try to swarm Kirby in certain segments.