Aw, man. I guess I'm not perfect. Well, now I've written the code for this (enabling checkpoints and not having it mess up your game) and it will be in build 24. Not sure how I feel about undo. If Erik says it's all right, we'll turn it on for play-testing.
BTW, we recommend a hold author does play through his entire hold normally before releasing it, with saving victory demos enabled. If you don't, and something's not beatable, the mobs'll get you
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Gandalf? Yes... That's what they used to call me.
Gandalf the Grey. That was my name.
I am Gandalf the White.
And I come back to you now at the turn of the tide.