With his IVs, he is very tanky physically and has a better Lightning Breath to take out archers. However, I can’t say the same for his res. Should I make him even tankier physically or make him a more mixed unit?
I would personally invest in his attack and defense over attempting to regain the resistance.
+def/-res is an excellent spread for physical and bow unit checking. Such specialization makes him really efficient, too. Any attempt of further coverage would result in him being less reliable.
It took me way too long to realise what you meant by F!Robin and why "she" had a boon & bane... Just refer to him as Grima or Grobin.
To answer your question, yeah, just go full Atk/Def boost for physical unit slaughter. If you happen to have any Fjorm or B!Ike lying around, they'll do a great job for his A; Vengeful Fighter for B; Ward Drag/Arm if in emblem team, or Thrt Def if mixed; whatever you like for seal if in emblem, but Boots if you're mixed.
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