I always try to fix a card by making it simpler rather than by making it more complex.
Auditor
Action - Attack - Looter
$4
Discard up to 4 cards. +1 card, and +1 card per card discarded.
Each other player reveals cards from their discard pile until revealing 2 cards which are either ruins or are not actions or treasures, and shuffles them into their draw deck. If they didn't have 2 such cards in their discards, they gain a ruins.
To my surprise, this version fits on a card pretty nicely, although it doesn't allow for any good formatting. It's still silly complex, though. If a player has to read a card each time to remember exactly what it does, it's too complex. I think even I would have to do that the first handful of times I played this card.
• Why put a limit at 4 cards? Might as well allow any number of cards.
• "+1 Card and +1 Card per card discarded" is a bit wonky. I think it'd be better if it were either just "+1 Card per card discarded" or "draw until you have X cards in hand".
• Having this crazy logic between three categories of cards (Ruins OR NOT [Action OR Treasure]) is a particularly difficult to remember piece of complexity. Something simple like "Copper" or "Victory Card" or just "Ruins" would be better.
• An attack that always makes each other player shuffle is not ideal. It's not awful, since it's not their turn, but what if this attack gets played 5 times in a row? Ugh.
EDIT: Here's another quick tip, having to do with your original version:
Auditor
Action - Attack
cost $4
Discard up to 2 cards. Draw 1 card plus 1 for each card you discarded.
Each other player reveals cards from their discard pile until revealing either a pure victory card or a $0 card. They put that card on top of their deck. If they didn't, they gain a ruins.
A "pure Victory card"? I'm not going to nitpick about that being undefined, when it's clear what is meant. But specifying that is a bad idea. I think I understand the thought process. You're trying to make it so Harem, Nobles, etc. don't count. But by making that distinction, not only are you making the card slightly more complex, but you're removing interesting interactions from the game. Hybrid Victory cards aren't very common, and it's cool that they help counter this kind of attack. In general, you shouldn't go out of your way to remove harmless interactions like this.