Some ideas for the challenges. Some i took from RA3, and some by myself.
1: Challenge with no hero restrictions/cap (exept irkalla and centurion).
2. The "Revolution" challenge for the Allied side. With enemy constantly sending super future tanks or regular ones at you.
3. "Mechanized" challenge.
The description: "Some lonely Chineese (can be any?) commander somehow managed to establish a Centurion assembly line in large industrial base(?), wich allows mass production of this machines. Eleminate the factory base, before he transfer this intel to other Chineese.", I might work description better, but here`s the main point: besides oblivious "core" of the challenge, there might be some additional "gimmicks" - enemy is able to produce vehicles really fast, and even maybe multiple vehicles from multiple factories at once. And yeah, enemy will produce/send apocs at you also, and even maybe super apocs (wich i doubt, by the lore), aaand... maybe, some kind of "supercharged centurion" as commander experiments on improving the basic centurion. But also all centurions can be "equipped" with Volkovs to aqquire tesla bombs and chain lightings, not Yunru`s (exept AI builds it). Or just "clear centurions" without infantry in it, or with just a cyborgs wich will shred all infantry. But there must be minimum of 4 in each wave, and more.
But the main "theme" about units: maybe enemy AI will only use vehicles, most of them are heavy, and extra only heavy infantry. And, as a bonus - enemies will send the terror drone waves at you.
And, when ill get the FinalAlert operational again - ill try to make the map for this challenge.
4. From RA3 - scavenger. Might not be a challenge, but the skirmish one. Basically, map is flooded with depiloted vehicles of all factions, (maybe without foehn), so, you can get engineers and capture vehicles.
Another one taken from it: "Behind the Iron curtain", but this time - shield generators. Basically, all your buildings in your base will be invulnerable, exept your Shield command at the middle. The bad thing is - enemies will also have this.
5. Chrono-challenge. Not a Timekiller, still its uses one faction, Euro Alliance. The idea of this challenge: enemy will constantly chronosphere units across the battlefield. I mean, he even can teleport his tanks in rear of your base.
This challenge strongly is based on "time tech and teleportation". Mass chrono legioneers, quickshifters, and chronospheres. And even if superweapons disabled, there will be a timer of "chrono reinforcements". Basically, enemy will teleport tanks on the entire battlefield. And it can be teleported in rear of your base.
Also, the longer you play, the stronger units will appear - firstly T1, and on. So, overtime, reinforcements becoming more stronger, and can posess a big treat to you. Also, theres not only one chronoshift, but a multiple ones, so, it can appear everywhere unless you installed inhibitors.
I hope you got the main ideas of that challenges
Thru, they are silly, but fun.