Well, I was playing with Horizontal Arrows for a couple months, so I’d say it was probably pretty good.
Like many assists, you can use it to allow you to get good damage with midscreen super jump glaive :qcf::h:, falling [:h:], land :qcf:[:l:], :h: :a1: :d::h: :qcf::l: :qcf::atk::atk:; the arrows keep them in stun long enough to connect Power Slash to Okami Shuffle, and that ender is significantly more powerful than anything else you’d be getting midscreen. Arrows does more damage than most things that you can do this with, too, because each arrow has a minimum damage of 12000.
It covers pressure well since even if people pushblock you its linear movement means they’ll still have to block it which gives you time to run up and 50/50 them with your unreactionable overhead and low or, if they don’t, time your overhead such that you don’t need to keep it going on hit with :df::h: :qcf::s:, which normally means you deal a lot less damage because :qcf::s: is a lot of weak hits, because the arrows will keep them hit enough that you can come in with some stronger air hits on your way down, even if you’re not in Glaive.
Then you have the more universal uses of Horizontal Arrows, to cover your approach and beat out other people’s projectiles as you advance without having to stop to reflect and possibly get baited by something, and to pretty much everything else it does. It’s a very good assist.
I switched to Vertical because, well, Vertical is also a very good assist. Forces them out of the air and into your mixup. People usually block at least two of them, so you can still have good stun time, if not as much all the time… And it gives you more time to visually confirm what your opponent will be doing when it comes down and forces them to respect it more than something they might be able to jump out of. But if you’re using Doom, you’re either using beam or hidden missiles, and if you have horizontal arrows, you probably aren’t also using beam… so I presume you’re using hidden missiles. So you probably don’t need that aspect, since you’re already forcing people to stay put and take your mixup with hidden missiles. Still, it is very cathartic to be able to take a step back after killing someone, call Vertical Arrows, and know that the moment the opponent comes in, the arrows are forcing them to the ground and into your mixup as the first action of the next round.