Kirby (SSB)/Down special
Kirby's down special move is named Stone, where Kirby transforms into a rock (an ability from most Kirby games) and becomes impervious to damage and knockback outside of grabs for the entire move's duration (exactly like a shield). While in stone form, Kirby can't move or attack until he reverts back to normal. Either simply waiting three seconds or pressing the B button will cause Kirby to revert back to normal. If the move is used in midair, Kirby will fall to the ground quickly; if Kirby lands on a sloped surface (such as the left side of Hyrule Castle) during the move or uses the move while standing on a sloped surface, he will slide down it. The Level 9 AI frequently does this move near this ledge, leading to SDing very commonly.
The move can't be used offensively while grounded, being unable to hit opponents unless Kirby uses it in the air and hits an opponent while falling. When he does however, it does 20% damage and great vertical knockback. The move is rather useful for countering juggling from opponents, especially air juggling, as the strong vertical knockback of the move can easily KO unwary opponents, or even more competent opponents if used unexpectedly. However, the slow startup makes it a bit less effective. Additionally, if Kirby lands and misses the opponent, the move has very high ending lag, even if immediately cancelled, being very easily punished by almost any move.
In terms of competitive play, it can be used to edgeguard Yoshi (albeit rarely) or other characters recovering from below at an angle (Falcon/Fox) but this is beatable by Smash DI'ing into the stage. It's also an unblockable attack if done on the exact edge of a lip (such as all the way on the left corner of Hyrule) as it will automatically hit twice, once on stage, and once while Kirby is falling.