Hey guys, I just wanted to weigh in on something that's coming up with some of the cards. As judge, I'll try not to give away my opinion on the cards themselves.
Some of the submissions give extra turns in interesting ways that prevent getting extra turns on their own extra turn (double shift, witching hour, sanctuary, voyage). As Gendoikari pointed out, technically these cards together could create an infinite turn loop. While it might be a good idea if you're Donald X to design cards that give you some flexibility to design other potential cards later on, for a design contest I think it's ok. I'm going to judge these cards only based on themselves (and the cards that actually exist in the kingdom).
That being said, I want to bring up a point that isn't exactly about unlimited turns but is somewhat related
Mission and Outpost have two key phrases in their text. "If the previous turn wasn't yours" prevents infinite turns. "If this is the first time you played mission/outpost" prevents you from getting more than one extra turn per round. Consider not just whether you can get extra turns on your extra turns, but how many extra turns you can get per round. 2 questions to ask yourself. For illustration I'm going to use an example Action card I've made up called Extra Turn which says "Take another turn in which Extra Turn has no effect when played" (it's not good, I know)
1) Can I play multiple of these per turn? (Yes)
2) If I utilize outpost and/or mission can I play this multiple times per round? (Yes. Play ET, Outpost and buy mission on Turn 1. Take outpost turn and play ET. Take mission turn and play ET. Take 3 extra turns). Note that while outpost and mission allow one extra turn per round no matter how many other extra turn cards there are, Extra Turn can be played multiple times per round (even if "if this is the first time you've played extra turn" was added) in the presence of outpost and mission.
It's not inherently bad to have a card that can get more than one extra turn per round. After all possession can do that. But it's something that will greatly change the relative strength of the card. Possession costs $6p (essentially more than a province). Even the best constructed outpost deck can only get one extra turn per round. If it could get more, it would have to cost more than $5. #2 is a lot less common to come up so it won't greatly affect the cost or how it's played (but is something to consider), but #1 will make a big difference.