If youre talking about the instakill that uses the saws and the overdrive nail gun that is patched out

with the ultraboost (core nuke) what happens is that you clip through the door this happens when you get right in the middle of the door when it opens and you just go straight through for shooting the core eject i recommend fully charging it and the looking directly forward while going down the stairs and when you get in the right spot of the door when you core eject you instantly switch to the malrail and shoot this pretty much makes sure that you hit the core eject

and i end up shooting it with the electric railcannon

is the electric rail cannon your first? If so, you could probably move your mal rail up in priority so you equip it first when you do railcannon

the way i switch to my rail fast is to before you leave the spawn room take out your mal rail before your shotgun so that its in the last used weapon slot so that you can switch to your malrail instantly and still have your elec rail in your first slot

idk how much you care about a tiny timesave but you can clip through the door that leads to gabe's arena which saves like 0.7 seconds. its a bit inconsistent but you pretty much just mal rail while youre centered to the door and it just pops you through. what i find makes it more consistent is not letting go of slide starting from the staircase all the way to gabes arena

Also if you fully charge your core eject shot you can switch to your malrail and shoot literally instantly just as fast as you can pretty much For the nailbomb you want to be standing on gabe's little chair and theres a certain lineup you want to place the magnets on. Watch my run and just copy where i place them and try to get that in your muscle memory it takes a bit to get consistent.

With the initial deadcoin you punched it 4 times which is not needed what you should do is after the 3rd punch you slam to the ground and get ready to started splitting the coin

The way you did your kill in your run is the way to do it, like in the right ideas sense it just needs some refining try just studying the top runs and just copying them thats what i find works

DO NOT USE MY RUN ON THE LEADERBOARD AS A GUIDE TRUST ME JUST USE MY 24.3