The two restrictions (that you have to enforce yourself) are simple: All craft must have a minimum speed of 0.10. The number of Frigates must be greater than the number of Cruisers.
This should hopefully get frigates more involved but still allow lots of flexibility in the fleet. Cruisers can’t dominate, but Beams become important again (as more than just clean-up). Fighters can’t swarm, but 101 pilots should allow for some bomber squadrons if you so desire.
Pure Frigate and pure Fighters are allowed, but not necessarily desirable.
Don’t retaliate; post any successful fleets as a Challenge for All.
Whoops! I used one of the Tribe backgrounds for this custom battle, so if the background is white it’s because you don’t have the Tribe expansion. It should still be playable, it just won’t look very good. I assumed the game bundled the background with each Challenge. Guess not. Sorry about that.