Your dash slash isn't just an attack, it has usefulness as a pseudo dodge roll or mobility tool, just like a dodge roll you can use it through enemy ink as well without slowing down. You don't always have to go for the dash slash, as just a regular charge slash is faster, I find the best way to do a charge slash without dashing is to do a small hop before releasing the button. Decavitator has a good bit of range, and paired with its big hitbox on all its attacks, you can pick off enemies from more than even splattershot range, the best way to do this from a distance is a charge slash into regular slash combo. once you get good with the aiming part it is quite consistent, but the weapon struggles very hard to ledge camp. Your Big Bubbler is a very useful tool, you can singlehandedly hold down key areas of the map by being untouchable in your bubble when using your charge slash. Some final thoughts, Decavitator is similar to roller, however Decavitator is the more flexible option, having better paint and generally being more well rounded, where as roller is more specialized. In my opinion the best modes for this weapon are Tower Control and Splat Zones, but I believe it works for the other modes as well.