In the near future, society switches to biodegradable plastic bottles, but conspiracy theorists think they contain autism, so some people switch to using glass jars for everything. The biodegradable plastic bottles... biodegraded... not long after the apocalypse. Now only the glass jars are left. You're welcome.
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I'm glad you don't want to punish the folks who log out. Yesterday, I had to log out of a server just as the sky was turning red, because it was legitimately time to go get my kid from school. Not everyone is just being a weenie when they log out for horde night. I actually came back later to find that everyone else had logged out and I was alone against the horde.
I like the idea of some sort of buff for surviving the night. What if there was an XP multiplier when you make a lot of kills in a short period of time? I used to play Fable, and it had a system where you had an XP multiplier that keeps getting higher as you land more hits in a row. Getting hurt or delaying between kills would push it back down.