Fair is the strongest and scariest kill move. The range is huge and it's safe, so it's a very good one. Imo one of thing that makes SlayerZ so good is the fact that he can get those Fairs better than anyone else at kill percent, scoring very early kills. Learning how to score a Fair is probably the most important thing (airdodge reads, spotdodge reads, or just outspacing them) in order to get kills. If you see your opponent has adapted, look at what they are exactly doing in order to avoid Fair (like staying out of range or doing quick attacks) and adapt back.
Fair is unfortunately slow so obviously it's not the only move you can rely on. Bair and Nair are both fast and safe moves so these are also quite reliable to use. Although they kill later you will have to use these moves a lot too, with only Fair your neutral game will become much weaker and quick attacks will simply stuff you.
Other than that, Dash Attack is a strong kill move. Be aware however that it is unsafe. I have a nasty Dash Attack habit myself and I get punished a lot for it. Nonetheless, it's still very good kill move because it's strong and fast (thus really scares your opponent) and it's very good for catching landings or for punishing unsafe attacks on shield.
Last is Bthrow, but it needs some kind of conditioning since it only kills early if you stand close to the blastzones with your back. You will mostly get Bthrows when putting ledge pressure on your opponent. Against opponents who like to shield when they get off the ledge, run past them and do a pivot grab to Bthrow. You can also roll to the ledge (so your back will be to the blastzones) while your opponent is on the ledge and shield. If they do a standard ledge get-up, you can grab or Usmash out of shield, if they roll you can dash attack or run Bair, if they do a get-up attack you shield it and grab them to Bthrow.
These are probably your most reliable kill moves, outside of hard reads with Usmash/Fsmash, but remember that at high percent pretty much everything starts killing. Uair is also a pretty decent kill move, especially when used close to the ceiling, and Ftilt can also kill at higher percents or with rage.
