Notably... *Selena* freaking came through again for me, sporting TA3 & Reposition, both of which are great for GHBs (despite Selena being pretty terrible for, say, Arena).
Actually... you can build a pretty effective Selena for arena; TA3 and Reposition are great there too. You just really want to give her a useful C skill (such as Hone Atk/Speed) because with her lower Atk she will act primarily as support, buffing and repositioning allies, while TA lets her check any green. She's basically a discount Eirika (who is absolutely one of the very best reds for the arena); obviously the lack of doublebuff is noticeable, but on the other hand Selena is highly available and can be built on a budget.
Clearly this week's bonus set was designed to make me eat my words. Cecilia was in the previous set of bonus options so Horse Emblem team with comparatively EZ perfects since Cecilia baits Rein / Bow-Lyn / etc. pretty well, but my only 5* option this time was Selena. But hey, variety is the spice of life. Also having a 5* Raven+2 (the Hero, not the Tome) with Deathblow due to IntSys being weird and never using him due to Cecilia existing was aggravating, so... super-mobility team-up of Selena / Olivia-Dagger / Tana / Raven go! Nobody can bait Rein or Lyn (no, Distant Def on -RES Olivia is not enough with her bad HP, not even with Res+2 Seal), but 3 Repositions, 1 Dance, and Guidance on Tana means that the team can YOLO charge in reasonably well for a non-Horsey team. -DEF, +RES Selena is largely a way worse Black Knight as far as being bait, BUT, she does screw Green Mages pretty well (eat it, Julia), and thanks to the new banners, there's a surprising amount of Armor Emblem going around, which she's hilarious against. Obviously eats Hector alive, and can potentially handle Black Knights with proper care and feeding as well.
Basically this team is worse but more interesting which is really the point. Oh, and speaking of Mobility, I threw Wings of Mercy 3 on Raven as well and put him on my defense team (still Tana/BK/Olivia-PA for the others). Enjoy, nameless Internet invaders out there.
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As a random bit of theorycraft, I kinda wonder where IntSys can go with future archers. They basically made the perfect archer stat profile in Bow Lyn - 3 Move, tons of Atk & Speed & Swift Sparrow, just enough Res to survive when killing a Mage that doesn't get OHKO'd. What else can they do to make future archers worth caring about?
* Jakob-Armor is throw a bow on an Armored unit and make it a tank, so there's that.
* In the same way, they can still do a Flying archer for Kinshi Knight air anti-air counter fun. (I'm not sure Reina qualifies for the waifu test, nor does Kiragi for the husbando test, though.)
* For the Astrids/Raths/Shins/Sues of the world... I guess they could do Bow Lyn's build but emphasizing okay Def and terrible Res rather than okay Res and terrible Def, which would be a (bad) sidegrade, but still respectable if you fear Archers more the Mages, maybe. A "balanced" horse archer stat build will just look bad at this point. They could maybe do a Takumi-esque horse archer who has a legendary with built-in Close Counter for some Archer capable of doing this in-game (Ranger Neimi? Paladin Astrid?), and that would have a place in more defensive teams...?
Basically they can try some weird gimmicks (for all that Lyn already has her own gimmicks in Mulagir & Sacae's Blessing), but it's tricky. Well unless they jump straight to Power Creep Round 2, maybe.