1. Just checked out that HUD element and I'll be honest, I've got no recollection of Splenderman or what that mode was meant to be...
2. The maps usually had multiple versions with tweaks, fixes etc. I remember for a short period a version of Mansion was available where I forgot to include the new flashlight vignette. Well done finding the bug!
3. Yeah, the 1 key was a debug feature to test different item counts without going around the level. Was meant to be disabled for production builds but seems some maps / versions have it left in