XP: 3.
Test Icons:

After you commit Copycat to a skill test, search the discard pile of another investigator for a skill you can commit to this test, and commit it. After this test ends, place that card on the bottom of its owner's deck.

Aleksander Karcz
Winifred Habbamock #30.

This card has interesting applications in supporting a teammate, as you are not limited to committing it to your own tests. An investigator’s deck typically has more skills suited to their own specialty than someone else’s. This means you can help out your guardian pal with their own Vicious Blow, recommit a seeker’s Deduction to their next investigation or even fill out a fellow rogue’s poker hand if one of their Aces ended up in the discard.

Kergma · 2
that's a clever idea. when i tried testing this i was mostly just using it to steal Eureka or Inquiring Mind from Minh's discard. it did work quite nicely for that. i even used it to get extra clues a couple times with Deduction — Zinjanthropus · 20
Not fully convinced that works. Copycat says to search for "a skill you can commit to this test" and you can't commit more than one card to a teammate's skill test, so after you've committed Copycat, no skill card is one you can commit to that test. Other users seem to have interpretted Copycat in a different way, suggesting that Wini wouldn't "control" the second skill card committed by Copycat, but I think given the card text states "you" can commit, the more natural reading is that you (the owner of Copycat) control and commit both cards. FAQ ruling pending! — aeongate · 62
After I commit "copycat" to a skill test,search the discard pile of another investigator for the "Leadership",and commit to the test. This test is successful. Can both two investigators gain 2 resources? — QQ5623 · 1
@QQ5623: I think that will depend on whether you or the other investigator is considered to be in control of the skill. My first instinct was that the one who is playing Copycat is the controller (controlling another investigator's card is not unprecendented), but others have cast doubt on that. I think we'll need to await a FAQ to be sure (or more likely have to send a query once the decks are released). — Zinjanthropus · 20

Buy this if you have Stella Clark in your team and enjoy committing Neither Rain nor Snow. Same goes with Nautical Prowess if Silas Marsh has managed to drop it.

Other than this, my favorite targets are Daring, Vicious Blow, Deduction, Brute Force, Expeditious Retreat, Sharp Vision, All In, Defiance, Fearless.

Big Iron · 30
I feel like Stella might be a little peeved that she can't bring it back with Resourceful or True Survivor any more. lol. Hopefully she has a Rabbit's Foot or something. Rise to the Occasion (3) also a very good target You'll get a guaranteed +3 on the test. — Zinjanthropus · 20
Probably even worse for Silas (and his Elder Sign), actually, at least there are 3 copies of Neither Rain Nor Snow. Silas probably won't get to see his Nautical Prowess for the rest of the game. — Zinjanthropus · 20
@Zinjanthropus I already played Stella with a Winifred who copied my signature 4-5 times a scenario with Copycat - you will see it many times. It's really not what I want to Resourceful anyway. — Big Iron · 30
You are correct about annoying Silas by putting it out of reach though, but that's what rogues do - they make people mad for selfish gains — Big Iron · 30

This seems like a really good card for winifred. +2 minimum, you get to draw a card and can get this one back. Yeah for a few rounds this probably wont be good at the start but once cards like steadfast or unexpected courage are played this really develops quick.

vosh · 9
Does this combo with Winifreds passive? Do you control the other investigators card and thus draw a card simply by committing this from your hand? — misterdavidjaques · 1
it does say that you commit it to the test, so i think it actually does. i hadn't actually thought of that. — Zinjanthropus · 20
Upon inspection of the rules, I don’t believe this works. Nothing in the card’s rules says that you control the skill committed. Cards in discard piles are underway their owners control, and cards enter play under their owners control unless otherwise specified. In contrast, see “You Owe Me One!” that explicitly clarifies a change in control. While I wouldn’t be surprised if synergizing with her ability is intended, RAW I see nothing that makes this work beyond inference based on an understanding of the word ‘control’ that goes beyond the defined rules of the game. — Death by Chocolate · 14
Ah, that makes sense. Another question is, does that mean that your team-mate is not allowed to commit a skill to the test if you're committing a skill (that they control) from their discard (with Copycat)? Looking forward to some FAQs on this. Will probably be some time. — Zinjanthropus · 20