fire boost on +hp/-atk Halloween Myrrh?

Burning a seal slot just so myrrh can utilize a boost better isn't a very good idea. You could instead give her attack +3 to fix her -attack and now you have more freedom with what you can do with her stats because of an empty A slot

where is valentine Ephraim please i need answers. my crops are dying

Its earth boost or bust tbh. Defensive boost skills inherently have more utility for multiple engagement. I would not recomend atk boost on myrh at all