www.paragonwiki.com Is a good site for all CoH information and it also has breakdowns of enemy group powers. It may take a little bit of fine tuning here and there, especially since some groups may act quite differently when mixed.
It can be a long read, but Paragon Wiki: Custom Units has some inside info and tips to creating balanced groups and such.
Creating a custom group for solo that's fun and challenging for multiple ATs is quite a task in itself, IMO. If you can pull that off... make it work solo for all ATs... then it should work great for a team as well.
A lot of this is all subject to Custom Group size, the bigger the group... the more freedom you have. 1 minion in a group of 1 that has a hold = lots of holds. 1 out of 5 minions that have a hold = much less annoyance and LT having hold ain't so bad.
Keep in mind, for the soloist... 3 minions in a group is normal... so in order to make a unique experience each encounter, you may want at least 4 minions.
Also, patrols can always keep a team on their toes.
Good luck!
Are you more interested in Custom Critter design?
Or selecting existing COH/COV/GR critters and mixing them together?
Mission Arc: Metatronic Mayhem (Id 1750): A tale of robots gone wrong, rogue robots gone right, and madmen gone every which way but loose.
I think for now, to keep it simple as this is my first attempt at making an arc, I'm going to stick with existing stuff.
So I'm trying my hand at this Mission Architect thing. I'm trying to create some Arcs for my VG to run. I want to make sure it will be a challenge for the most amount of people possible. Is there a post or a site that outlines enemies strengths and weaknesses? I'm trying to make sure that our team would have to actually work together and that everyone would have a part to play at various times. I have no problem combining multiple enemy groups to make this happen. Any help will be greatly appreciated.