My main formation
This is the main formation I use for most content.
Abraham is the usual MVP. He can stay at the back or frontline positions but I personally like frontline with Magna so I can pull 2 backline (usually high priority targets). Belle stays at the corner where Abe is so she pulls the furthest enemy, meaning Abe gets to pull ALL backline characters. Kate is in corner position but will depend on what enemy position you want to target with her green targets to share damage as Abraham and Belle decimates them with AoE damage. Magna is mainly used for her speed boost to let Abraham not get interrupted during his pull. Last but definitely not least, Eugene with his amazing scarecrows (better with Personal Gear) to taunt high threat targets while clutch healing the team.
Hope this helps! It’s not the best on certain enemy compositions but it really helped me grind through most stages! Would love to get constructive criticism as well regarding weaknesses and replacements if ever! Thank you!