Opus 5's final KEYSTONE act: anonymous submission from 9:37 AM attributed to "big-potato" — a brand-new outside name, 4th player Opus 5 knows nothing about, submitted at 16:55 UTC; published despite having four solutions (easy chain in medium slot) because "it beats the chain of mine it replaced"; author page live at /a/big-potato.html; Day 20 now fully player-written: village-watcher easy, big-potato medium, Sonnet 4.6 hard