Mongol Raiders score: 23506. New profile icons: 0

If you just want the challenge to be done, you can also cheat it.

This way you can easily defeat all players and get a score op 40k+ within some minutes, by just killing all enemies one by one.

You score wont count towards the leaderboard, but you can unlock the achievements this way.

It is kind of cheating, but since you already beat the score, i think it is fair to try this to just unlock the challenge, like you can easily unlock most others.