My submission is a split pile (with the bottom card being the attack):
(updated versions explained
here and
here)
(older version)
(original versions)
$2 - Treasure
$1
+1 Buy
-
While this is in play, when you gain a card costing $3 or less, you may gain a copy of it.
$5 - Night-Attack
Each other player reveals the top 3 cards of their deck and trashes a card costing up to $3 that you choose. Choose one: gain a card costing up to $3 per Clutter you have in play; or gain a card from the trash.
Clutter can make a mess of your deck if you take too much advantage of its "while in play" effect. However, there are many Village variants that it helps you gain quickly, as well as other $3 or even $2 cards (Lurker, Fool's Gold, Page, Peasant, Encampment). The +1 Buy can make this gaining (of deck-cluttering cards) even more powerful, if you want.
Cleaning is generally a reference to cleaning out other players' decks, but it can also relate to dealing with your own clutter (in a positive way, though not getting rid of it). If you can get 3 of the 5 Clutter cards, you can even use Cleaning to gain a Province or Platinum! And while you can use Cleaning to steal Clutter from other players, they are also going to be trying to do the same from you. The trash will usually have cards costing up to $3, but if you can match your Cleaning with even 2 Clutter cards, that can get you a Gold or other $5 or $6 card from the Supply instead of digging through the trash.
While designing these cards, I went through a number of different options, but my thought was a split pile, right from the start. At first, Cleaning was going to be an Action-Duration-Attack, which stole from some set of cards when someone played them, but I couldn't find a good balance. Then, Clutter was going to be an Action card with +1 Action, +$1, +1 Buy and the "while this is in play" clause, allowing Cleaning to be a Treasure-Attack (so Clutter is played before Cleaning). Once I realized I could shift that Cleaning card to be Night-Attack instead, it was an easy switch to make Clutter a Treasure, allowing them to be played more reliably.
I was getting close to the current versions, but having troubles with them. I briefly considered having Cleaning be its own 10-card pile, with Clutter becoming a non-Supply pile, likely with 20 or 30 cards. Cleaning would look at other players' cards like now, but return any revealed Clutter cards to their pile; and it would have gained a Clutter as well as a card costing up to $2 or maybe $3 per Clutter you had in play. Unfortunately, that forced gain could result in getting a Copper if you had no Clutter in play, and some decks would be able to gain Provinces too easily. So I ended up back at the split pile, and added the choice for the gain, landing where the cards are now.