Hríd's best friend.

B!Veronica.

Keep Close Guard or give her a cav buff on C skill.

Do you have Gunnthra? Those skills work in tandem with each other, as Gunnthra debuffs the one with the lowest Def and Hrid hits the lowest Res unit. (Unless the unit that they both hit happen to have both the lowest Def and Res of the team, of course.)

You could also try Arvis or Saias, both having Ploys built into their weapons. They are also pretty accessible with the Grails if you don't already have them from past GHBs.

Arvis, Saias, Katarina, Lute, Gunnthra, Brave Veronica, Sothe, Soren, Lilina, Easter Catria, Easter Sharena, Surtr, Aversa, Male Morgan, Loki, Clarisse, Legion, Spooky Henry, Spooky Jakob, Fallen Takumi, Gharnef, Non-Pain+ Healers, and just about any other dagger unit will all work well for Hrid.

I'm still waiting on a Double Chill weapon, though.

Veronica and Gunnthra are great choices, especially since they’re both cavalry and can give him access to cavalry buffs. I also have a double ploy Priscilla but any unit with high enough res to run ploys is a great choice.