Mr. Game & Watch (SSBU)/Up smash
Mr. Game & Watch will perform a headbutt while wearing a scuba diver helmet, referencing his game Octopus. The move is one of the most powerful of its kind dealing high damage and knockback which makes it a viable KO option and it also has a fairly large hitbox, giving it deceptive range. Its startup is rather high as it comes out on frame 21, but in contrast its endlag is extremely low as it only has 13 frames of cooldown which is excellent for baiting the opponent and makes it very difficult to whiff punish. In addition to its very low endlag, it grants Mr. Game & Watch invincibility during the hitbox frames which makes challenging the move extremely risky as the opponent could potentially get themselves KO'd while Mr. Game & Watch remains completely untouched.
Lastly, the move has two more strengths. The first of these is its combo starting potential at low percents. Due to the low cooldown, the move can lead into combo extending moves such as neutral aerial, up aerial, or Fire. The second is its extreme safety on shield. Due to the move's high startup and low cooldown as well as its relatively high shieldstun, it is -6 on shield when fresh which is very safe for a smash attack.
Overall, it is considered to be one of the best up smashes in the game due to the move's high power, very low ending lag, invincibility, combo starting potential, and safety on shield which makes it a very useful tool in Mr. Game & Watch's kit, although its slow startup can make it difficult to land sometimes.