King K. Rool (SSBU)/Back aerial
A slow, but powerful backwards punch. King K. Rool's back aerial is notoriously powerful, being able to KO at extremely low percentages be it in the air or on the ground. It is also disjointed, with the fist not being a hurtbox. It has a meteor smash for aerial opponents only, which KOs as low as 40%, as well as a powerful grounded hit that can KO at around 110% with optimal DI. The hitlag is low as well, combined with an odd angle, which makes DI difficult. This often makes the move seem to kill earlier. It does however have a mediocre sourspot with higher hitbox priority, meaning spacing is required to make the most of the harder hitting hitboxes. Overall, the KO potential of back aerial cannot be understated.
Back aerial has formidable range, long and far out of what the animation would suggest. This makes the meteor smash very formidable and have a wide threat range once used, allowing for K. Rool to position himself during the initial lag and set up for the KO. This is often used against characters whose recoveries either have poor hitboxes or none at all, such as Mario or Donkey Kong who have issues contesting it in these scenarios. If threatened offstage, using back aerial preemptively can lead to reverse edgeguard situations, ending stocks while in disadvantage.
K. Rool players tend to use back aerial as a hard punish in neutral, often while retreating so to increase the potency of the disjoint. This is due to the large active frames while being able to use the initial lag to position K. Rool. This allows for it to KO grounded opponents early or hitconfirm at lower percentages, or act as a kill confirm enabler against aerial opponents, namely in tandem with up aerial. It is very committal however, making it difficult to justify using on a regular basis. Overall this makes back aerial a decent defensive option.
Back aerial is reasonably safe on shield due to the enormous hitbox and power, making it just -7 on shield landing. By spacing it properly, due to the shieldstun and K. Rool's movement trajectory, it is very difficult for many characters to punish; it can notably be used to space against Cloud's Climhazzard out of shield. However, it is extremely punishable prior to hitting shield due to how reactable it is, meaning careful precision is required if a player uses it in this way. Generally, it's rare to see back aerial be used in this fashion in tournament-level gameplay.
Back aerial allows for niche combos at 0% if the sweetspot hits, with it being +18 on hit if landing. This enables dash attack and forward tilt as potential combos in-context (though the launch distance makes it difficult), which can be very damaging. Forward aerial can be used as well, but it is difficult to use in this scenario, and the reward on hit isn't as high outside of setting up platform tech situations.
However, back aerial has many drawbacks. It's extremely slow, with 17 frames of startup lag. This allows for many characters to out-frame the move should they see it coming, in addition to it being painfully reactable and easy to perfect shield. Sheik is a good example of this, with enough mobility and frame data to easily use a stray back aerial as an opportunity to get in. While it can be safe on shield, characters with long-range options tend to have an easy time against if if K. Rool doesn't land perfectly. It is also very punishable on whiff, with 14 frames of landing lag and a very high FAF of 60. Thus, back aerial is better off as a hard punish, surprise option or off-stage kill tool.