1 Ulmer, 2 Valen and 2 Gatos is what I run personally for my blue stacks on challenge events and raid tournaments.
Valen -> Gato is a deadly 1-2 punch, since they’re both the same color and speed they always charge at the same time. Super easy to set up and deal lots of damage with
I’ve got dupes of Mnesseus and Berden myself, but only because I lack Hisan from Sand event. If I had Hisan I’d easily aim to have 3 of him + Muggy + Brienne for my green mono team
I have dupe Melia as well, for my mono yellow team I run 2 Melia + 3 Banes. I know other players choose to just have 1 of her though and run 4 Banes instead.
Her tile damage is high and the crit bonus makes it insane. Also the family bonus thing only works for each unique hero though, so you’d have to run Mnesseus with her on a 3-2 stack.