I've tried to make an Un-set Cube like 3 different times, but if you go by the traditional model of only 1 copy of a card and only un-cards, you'll have a really weird and bad cube. Unstable was certainly a step in the right direction, but it's a bummer that two of the main mechanics (Contraptions and Host/Augment) are incredibly parasitic for cube, if you want both of these mechanics then you have to break singleton or create new custom cards to make it playable.
Here and
here are stuff on unstable and parasites
You'll also need
this tool if you want to go down this route.
If you DON'T want those mechanics (like I) then you'll need to look at other sets to find that goofy magic humor. Cards like
Goblin Game,
Meteorite, and
Goblin Balloon Brigade work, but
humor is subjective they're hard to find, and most are likely on the lower power level, definitely not as playable as say using
Magical Hacker with a planeswalker (I wouldn't recommend making a
powered cube with un-cards, but it does sound like broken nonsensical "fun".
I'll probably do this for the heck of it after I finish my current cube project).
(Oh yeah, you can also replicate the draft experience of unstable
like so, which are certainly a lot of cards, but can't say it doesn't work)
Here's one of my attacks at the cube,
here's my most recent one with the recent set being modern horizons. Both of those are incredibly rough and not even close to finished (I remember having a 3rd attempt, but I can't find it, so I either deleted it or misremembered)
From my own experience with trying to make an un-set cube, I garnered that for the amount of effort I would put in for trying to make a fun varied drafting experience I realized that while many of the un-cards are
cool there's just too many of them that are way too
rules heavy with
obtuse game mechanics (and a few
"unfun" cards as well) that in the end the only person that would enjoy drafting the cube in my play-group... was
me. So I gave up on it. But if your player group enjoys that type of fun then by all means go for it! I have a deep love for the un-sets so don't let my experience bog you down, I'm just trying to give you a fair warning. Happy cubing!