This sub-game is stated to be a sort of "what if" scenario or alternate universe/timeline; the same is likely true for the other Meta Knightmare sub-games.
Meta Knight retains many abilities and attacks from Meta Knightmare Ultra. He is able to use Galaxia (which applies fiery effects) and the Knight Spin (which applies icy effects). Special Moves from Meta Knightmare Ultra also return. Meta Knight has new attacks as well as slightly more power and speed than before in this sub-game. Some aspects of the sub-game are carried over from Kirby: Triple Deluxe's Dededetour, such as the regularly spaced save room checkpoints, and the presence of stronger versions of bosses,
Meta Knight can accumulate Meta Points (by defeating enemies or gathering them from the environment), and can store a total of 50 points. He can spend these points to use these moves:
Meta Knight's movement speed is increased for a short period.
Completely replenishes Meta Knight's health.
Meta Knight unleashes a powerful close-range attack with Galaxia.
Meta Knight summons members of the Meta-Knights for a devastating full-screen attack.
Differences from Story Mode
There are fewer recovery items in this mode. Some of them have been replaced with other items.
Point Stars are replaced with collectables in the shape of Meta Knight's emblem that have the same function.
Enemies are more frequent and can appear in varying sizes.
Stages are compiled in one level and at the end of each, a time will be shown.
As in Kirby: Triple Deluxe's Dededetour, each level contains two save points that also refill all of Meta Knight's lost health. One will be near the halfway point of the level, and another will be at the end. In the case of Level 6, its second save point is located just before the boss. The save switches are decorated with Meta Knight's emblem, and the save rooms are all set inside of a gigantic hangar in which the Halberd has been docked.
Kirby takes a nap during the events of this mode, explaining his absence from the sub-game's story.
Similarly, Meta Knight also has techniques that share names with his regular special moves from those games, including the Mach Tornado and Shuttle Loop. This is to be expected, however, as his move-set in Kirby's Return to Dream Land is nearly identical.
Unlike previous games in which he was playable, Meta Knight rides Warp Stars like Kirby in this mode instead of flying on his own.
Despite the fact that Meta Knight lost the ability to glide after using Shuttle Loop in Super Smash Bros. for Nintendo 3DS and Wii U, he regained it for this game.
Unlike in Dededetour, there are no added shortcuts, perhaps due to them being deemed unnecessary with Meta Knight's greatly superior speed.