I was playing Blaise End, and as I was rebuilding my Scavenger Room (I sold it to make imps to gather gold to spam Lightning) after I won, and then I remembered once playing in Skybird Trill. I didn't know how the Scavenger Room worked, so even after there were no Horned Reapers, I kept on scavenging.
I had three level 10 Horned Reapers, one from the Transfer Creature, one was the neutral creature, the last I converted from the heroes. They were scavenging for a while, and I thought that I could get more but after a long period of time, since there were none from that level.
And eventually, I was right. I saw a single level 1 Horned Reaper appear after scavanging for as long as it took to get a level 10 (Maybe more). Is this a glitch or what? I was playing the normal Dungeon Keeper, by the way.