I'm least satisfied with Mushroom Kingdom Meltdown 1. It was just unpolished, laggy, bad plot and just not very fun in my opinion. But I remember that was pretty much my first full length multiple exit game I ever made.
The hack I'm most satisfied with is, 2 Player Co-op Quest surprisingly. Mainly because I think it has a unique gimmick which I don't think any other hack has, where 2 players can play at the same time. It was created by using a very old IPS patch called Project Bottles. Player 1 and Player 2 play against each other, but at the end of the game work together to win.
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