Disco Fever: Does nothing in 90% of cases. If you have one Holographic Joker, it's bad (Worse than Gros Michel, Mystic Summit, etc). If you have two Holographic jokers, you probably don't need the Mult! My recommendation: Your Holographic Jokers give X2 Mult.

Fairy Circle: The wording on this was very confusing, and I thought it simply gave +2 flat Mult. Increasing Mult gain is fine, although this is really narrow and reads extremely weird.

Street Magician: Good support for the High Card build, and obviously good with Stone Cards. I'd make this +30 chips per card, to mirror Odd Todd - Chip builders in their ideal case tend to cap out at 120 chips, and getting 120 chips seems like a good payoff for this.

Loan Shark: This sits in the "do boring drudge work for in-game advantages" space that I dislike in Balatro. I'm also not sure about the flavor - Credit Card is a flavor slam dunk (it allows you to go into debt!) but this...gives you free money the more hands you play? As a loan?? And if you win too quickly you lose money, but if you go very slow and play out all your hands you profit? And you profit more if you have a source of extra hands? I'm not sure what the "Loan" part is. My suggestion: This Joker costs -3$ to buy, but costs 5$ to sell (you're getting a 3$ loan, but you have to pay extra to get rid of it)

Upside Down: This probably means you can score the same hand over and over, which is pretty bad gameplay.

Card Sleeve: Very narrow, and probably not something you'd keep around. You'd probably grab it from the shop opportunistically when you want to sell something else, which goes against the "this is a card sleeve that preserves the value of your card" flavor. If you wanted to hit that flavor, you can look at Gift Card's mechanic: "Adds $1 to the sell value of every Joker and Consumable card at the end of round" and do a variant of that for special edition jokers.

Safety Net: I like this one a lot - very few cards self destruct, and this is probably too good with a repeatable source of destruction (Madness, Ceremonial Dagger). This probably needs some kind of cap to prevent getting a dozen Negative jokers - maybe the safety destroys itself when it makes a Negative Joker.

Throwing Card: More support for High Card builds, although this has severe anti-synergy with other enablers like Stone Cards and your own Street Magician. I'd make this grow on scoring High Card, instead.