Why this page exists: A player wants the documented challenge loop and needs the achievement caveat separated by version.
The launch loop
The official launch post describes 24 challenge scenarios, with five available immediately. Completing them awards points used to expand access, and higher difficulty raises the point reward.
The same post says a random ability is added to the starter for each challenge, so the opening condition is not a fixed universal loadout.
Read the achievement notes narrowly
v1.0.2 says unlocks and achievements cannot be earned in challenges. v1.0.3 then says challenge achievements work. The safest interpretation is to distinguish general rewards from achievements designed specifically for challenge completion.
That interpretation still needs a current-build check. This guide does not flatten the two patch statements into a broader promise.
No invented challenge tier list
The official sources do not rank the 24 challenges or publish a best starter for each one. A tier list would need recorded runs and versioned evidence, which this site does not claim.