FINALLY PATCHED
can be done with a 2nd (silver)account
have a friend create a challenge -just beat wave 1 on 1st arena and die on 2nd wave,then send it to you
not sure if you could just die 1 wave later,to be safe i did 5 more waves til it says -victorious- then bounce back the challenge (and have u´r friend fail on it-just die on 1st wave) --that´s how i did it- but achievement popped right after i bounced back the 10th, so i guess that´s not necessary
do that 9 more times,with the same or different friends and it finally popps---i used my 2nd account
mystic weirdo confirmed you don´t have to play til it says "victorious" and just need to do 1 more wave
dashboarding and restarting the game usually makes the challenge status between u and u´r challenged friends update faster, sometimes also the leaderboards, but those sometimes just need a day to show the real number of won challenges