As reward for killing Patchwork Juggernaut under 4 minutes, you should get the Mask of the Sleepers, brown. I did it and get an achievement. What I didnt get is, howewer, reward.
It looks like something has broken in the awarding of this particular clothing item. We’re looking into a fix. When fixed, we will make sure everyone who has already earned the achievement will get the clothing at that time.
Sorry for the inconvenience, and thank you for reporting this!
Sleeper's mask (brown) not appearing as owned in dressing room