I might just make a general AT concerning the lag that can be avoided by catching the boomerang. In smash 4 the amount of time spent catching the boomerang is significantly less than it was in Brawl. In Brawl the idea was always to avoid the catching animation pretty much at all costs. There were some known ways that catching it could benefit you, such as cancelling the extreme landing lag of Dair, but beyond that, catching the boomerang was a hindrance.
Now however, we may want to re-think this.
Catching the boomerang takes only 9 frames in smash 4 (this is so for both the custom boomerangs as well), meaning that if timed/positioned right you can cut out lag from many other things.
Dair has 40 frames of landing lag, but we already knew that would be clearly beneficial.
Fair has 17 frames of landing lag, so catching the boomerang at the perfect time as you land can almost half your lag.
Uair has 21 frames of landing lag.
Bair has 22 frames of landing lag.
Nair has 12 frames of landing lag, so while technically you could shave off 3 frames, I don't think it's worth trying in practice.
Zair only has 8 frames of landing lag.
Airdodge has 21 frames of landing lag. This means that if you airdodge into the ground, airdodge then Zair, or airdodge then Zair while holding a bomb, you can cut out over half the landing lag if you catch the boomerang upon landing.
As for catching the boomerang while running to allow you to dash back in the opposite direction, if this is what you want to do, then the only alternatives out of a run are to do a dash turn or to dash back after a skid. A dash turn takes around 24 frames to really get going in the other direction while dashing back after a skid takes 19 frames, so there's a definite improvement there too if speed is what you're after. It would be better if this was thought of more generally though, so instead of just being a way to run back in the other direction, it should be thought of as the fastest way to return to neutral (with all options available including dash) out of a Run. You can of course do certain actions directly out of a Run however so catching the boomerang out of a Run will not be the fastest way to do everything out of a Run, just some things.
As for actually applying any of this, at this stage I think that the fast boomerang may actually be the way to go simply due to the fact that it always follows a direct path back in the direction it originally came from, and because of the fact that it will always require the same timing because the boomerang will always go forwards the same distance even if it hits, and because it's so fast meaning there's more chance of it being caught immediately after landing.
Actually this is pretty cool.
With the fast boomerang you can do stuff like smash throw forwards, immediate SH aerial (e.g. Fair) FF if necessary and you immediately catch the boomerang upon landing, and there really is a notable difference in lag.
You can also throw the boomerang forwards then run at it and do e.g. U-tilts/Jabs/F-smash forwards seemingly straight of a Run, which is pretty cool, and if you're using the fast boomerang it means you can always get in nice and close to the opponent for when you catch the boomerang.
Fast boomerang smash throw forwards to immediate backwards SH Airdodge to Zair let's us land with the 9 frames of boomerang catch lag, similar to our normal Zair landing lag, which bypasses the airdodge lag nonsense.
It's worth looking into imo.
Check out their matches. Then you can see why and when to use them also.
