I would't make it that hard.
Group A
- Lion DS 9 (highest)
- Wolf DS 7
- Frog DS 2
The DS of this group will calculate like this:
Keep the highest DS, the lower will count as 1
Highest DS + 1 + 1
The DS of group A will be 9+1+1=11
- If roll 13 -> kill a frog (2), lion is (9-2=7), wolf is (7-2=5), so new group DS is: Highest DS (7) + 1 = 8
- You roll 15 and kill'em all
it makes it harder to fight the group, because they get +1 for every additional member but it's still fast, because you only got one roll against all of the enemies.
In Advanced Dungeon Goons it works similar but you still got to fight against every enemy separatelly, so you they get +1 modifier to DS for every adittional group member, but you roll against every one. In our case:
Lion DS 9 + 2 = 11
Wolf DS 7 + 2 = 9
Frog DS 2 + 2 = 4
And you roll against a frog, you roll 6 and you kill it. Now you roll against a wolf that is 7 + 1 (because the frog is killed now), and so on.