Meta Knight is more or less a Sword/Wing Kirby Glass Cannon hybrid.

General

• Because of his innate ability to fly, many co-op strategies involve the main Kirby riding on Meta Metaknight.
  • However, there is a misconception that flying over everything is the fastest strategy for levels. Meta Knight flying is still only horizontally as fast as running on flat ground. This means Condor Head, Burning, Wave Surf, Tornado Attack, Cutter Dash, and even Slide Attacking are all faster than flying. Therefore, Kirby riding on Meta Knight's back should only happen when a Wing Kirby would fly in a solo-run.
• While flying with Meta Knight and Wing Kirby are functionally the same, Wing Kirby flaps when either up or 2 are pressed. Meta Knight only flaps when 2 is pressed, so mashing up on the d-pad does not help for Meta Knight.
• Generally, Meta Spin Slash gives the easiest, most consistent DPS against grounded bosses/minibosses.
• Shuttle loop is jump-cancellable. This means that Meta Knight can use shuttle loop, flap once, then shuttle loop again, giving excellent DPS better than Wing Kirby's Dive Bomb (but it is very difficult and straining), even factoring in damage reduction. This should be used against all aerial bosses/minibosses, and taller grounded bosses.
• Thanks to his excellent power in both spin attack and shuttle loop, and his innate ability to fly, Meta Knight is generally one of two ideal co-op characters to use for most co-op speedruns (the other being a second kirby)

Character Differences ^[1]

• 10% less HP than Kirby
• Shuttle Loop forces Meta Knight to enter a glide state whereas Kirby can't glide after Upward Slash, but can optionally follow up with Sword Dive
• Can do Condor Dive whenever he wants whereas Kirby can only do Sword Dive after Upward Slash
• Can do Up Thrust
• Meta Knight has the same basic ground sword combo as Kirby plus an additional 2 attacks between Kirby's 1st and 2nd attack
• Flying as Meta Knight is identical to Wing Kirby's Hover Flap. Overall, this makes him vertically the fastest
• More damage on most attacks than Sword Kirby

Moveset

Overhead Slash (Press 1)

• Attack properties ^[1]
  • Near Hit - 18 dmg
  • Far Hit - 16 dmg

Knight Beam (Press 1 at full HP)

• Attack properties ^[1]
  • 16 dmg

Meta Triple Slash (Press 1 twice after Overhead Slash)

• Attack properties ^[1]
  • 1st hit is NOT comboed from Overhead Slash - 16 dmg
  • 1st hit IS comboed from Overhead Slash - 14 dmg
  • 2nd hit - 16 dmg

Meta Multithrust (Mash 1 after Meta Triple Slash)

• Attack properties ^[1]
  • 1st hit is NOT comboed from Meta Triple Slash - 8 dmg
  • 1st hit IS comboed from Meta Triple Slash - 7 dmg
  • 2nd, 3rd & 4th hit - 7 dmg per hit
  • 5th hit is NOT comboed from 4th hit - 16 dmg
  • 5th hit IS comboed from 4th hit - 14 dmg
  • Entire combo (Overhead Slash + Meta Triple Slash + Meta Multithrust) does 90 dmg max

Piercing Slash (Dash + 1)

• Attack properties ^[1]
  • 1st hit - 12 dmg
  • 2nd & 3rd hit - 10 dmg per hit
  • Max total - 32 dmg
  • Lunge at a foe from a bit of a distance to do a combo
  • Invincible for the duration of the move

References

1. ↑ ^{1.0 1.1 1.2 1.3 1.4 1.5} An ability and damage guide at the Kirby's Rainbow Resort forums. It's mainly maintained by Plas Durock and contains contributions from several members of the Rainbow Resort forum and the GameFAQs KRtDL forum. http://www.gamefaqs.com/boards/935607-kirbys-return-to-dream-land/62398037