4x 5* MERRIC KILL ME PLZ @@@@@@

Well, if you're willing to invest, here's the best Merric exclusive build I've been able to come up with so far. This is all in theory - developed using the kagerochart damage calculator - but when I finally pull a +ATK/+SPD Merric I'll probably give it a go.

IVs: +ATK/+SPD, -HP
Weapon: Excalibur
A Slot: Life & Death
B Slot: Green Tomebreaker
C Slot: Flexible
Special: Moonbow
Seal: Quicken Pulse/ATK+2/3

Excalibur is a good tome/weapon 14 attack and advantage against fliers units? Worth it.

Merge them and make your +Atk -HP one a god amongst Merrics. Mine has the same IVs and he's great.

My Merric is ATK + and RES - and he holds out pretty well against other units. I am considering running Gronraven on him for a Decent Lyn Counter since I have no one else. I am also running Death Blow 3, Bow Breaker, and Threaten Res. Also Sol to keep himself alive and Draw back as support skill. Just experiment with him. He (with Excalibur) nukes every flier except Palla with Ruby Sword. If you have trouble with flier emblem, then run Merric with Excalibur. He is not as bad as you think.

You could make him into an Anti-Blue/Bow unit.

IV: Any except -Atk
Gronnraven (Gronnraven+ if no +ATK)
A: Triangle Adept 3
B: Quick Reposte 2/3
C: Flexible
Special: Ignis
Seal: Distant Defense

Merge them into that one and you have a nice bait unit that will not only survive but KO Honed Rein +10 & Honed B!Lyn +10 with some very minor exceptions.