Add some monsters worth 4 BP and a potion of healing, or monsters worth 8 BP and two potions. Something like that.
I once made monster group cards so that I don't have to think about it when the opportunity arises.
Sorry, deep linking from Imgur doesn't work anymore on mobile phones.
This is an Orc Monster group for 4 BP
https://imgur.com/a/4uUnW9j
This is a Goblin group for 4 BP
https://imgur.com/a/ak0M3KU
This is a Monster Boss that'll cost 4 BP
https://imgur.com/a/rDoRLyo
And this... can't remember if it was 2 or 4 BP, but those skeletons all have a spear so I guess there are not loads of people who will use it besides me.

https://imgur.com/a/w6Nxomz
All of those are: green for Heroes with 2 dice, yellow on top for Heroes with 3 dice, add the red for Heroes with 4 dice, add the purple one for heroes with 5 dice. Or Heroes with 4 dice and 4 Mercenaries.
Except for the boss monster, there you choose only the appropriate color, you don't add them.
