Custom challenge mode for campaigns

[dragos]

Increasing the difficulty by increasing the strength of all enemy units does not feel right to me, so I came up with a system that increases the difficulty in a more realistic way: restrict units available for purchase.

So we have 6 classes for ground units (Inf, Recon, Arty, Tank, AA, AT) and 4 classes for air units (Recon, Ftr, Tac, Str).
At the start of a scenario, a limited selection of units is offered for purchase in the following way:
Roll 3 random classes for ground units, then from each class roll one unit (I use an online list randomizer tool for this).
Roll 2 random classes for air units, then from each class roll one unit.
The result will be two lists containing 3 random ground units and 2 random air units (each from a different class).

For example for ground units you have:
- German Engineers '39
- SdKfz 232 8Rad
- 37mm Pak 36

And for air units:
- Arado Ar 196
- Bf 110 C

Once you purchase a unit from one list, the units in that list will be re-rolled.

This will make an interesting challenge instead of artificially increase the strength of all enemy units, as you are forced to play with a sub-optimal core, with some units you usually never pick, but it feels more realistic.

At the start of a new scenario you are allowed to upgrade any unit that carried over, but any new purchase is subjected to the rules above.