In addition to the considerations of the level 0 Robes, which I've written a review for, for 2 XP you get the following:

• Cost is reduced by 1
• A icon for your trouble
• "Playing that card does not provoke attacks of opportunity."

That last one is the big ticket item. We've all been in this situation: you didn't get Shrivelling in your opening hand, your apprentice is truant, and then you finally draw it during Upkeep, just for an enemy to spawn on you in the next phase. In the past, you used to dread these situations, especially if that enemy had some other nasty Forced effect if it hits you. Now you just laugh.

Sadly, these robes have the disadvantage of being in the Mystic card pool, which tends to be the most competitive in terms of upgrades. Of course, you can always Delve Too Deep or do a little Arcane Research.

EDIT: The cost reduction is actually also really nice and worth emphasizing. You're not just saving 1 resource on this upgrade--you're lowering the buy-in for a card that saves 1 on the first spell you play per round. That's a lot of savings.

DeathbyChocolate's inspired jankery aside, 4 XP and 4 Resources are nothing to sneeze at, but a more or less guaranteed 9 damage, plus bonus effectiveness from Oops!, Oops! (2), and/or Act of Desperation allowing you to get maybe 20 damage across 2 turns is pretty good for a Survivor combo. And, with Scrounge for Supplies and Resourceful, you might be able to get most of the parts of the combo back in your hand for another go.

Slightly more seriously, comparing it to Old Hunting Rifle, its +1 XP, + 1 Resource, and -1 seems about right for its considerably better consistency. I have my doubts the 1 Damage Fail effect will be used much except in dire emergencies, but it's nice to have options.

I don't see Ashcan, Wendy, or Patrice packing this (although a chainsaw in a viol case is a striking image), but Silas and Yorick might well consider a trip to the hardware store, with Stella and Rita more on the fence.

After running Chainsaw Yorick for a few weeks, let's consider the case of Chainsaw Yorick:

Good Stuff

• He is a beast with this thing. 3x 6 3 damage is very nice. He demolishes most normal enemies with ease and can take on Elites and Bosses like, well, a boss.
• It combos very well with Act of Desperation and Live and Learn, getting hits in and reloading the damage machine.
• With his access, Tetsuo Mori, and Prepared for the Worst help you find the saw, and Vicious Blow and Vicious Blow (2) and help you deal with 4 and 5 health enemies. Well Prepared works amazingly well with the Chainsaw's out. (If you can get Veda Whitsley as an ally, she;'s amazing, too.) A singleton Scene of the Crime has been very clutch.
• Yorick's ability works very well for juggling saws, as long as you can find a 2 Health enemy to kill with Act of Desperation. His ability gets other stuff back from discard (supplementing). Resourceful

Bad Stuff

• It's hard to keep Yorick's resources where you want them. If you can finagle enough Act of Desperation plays, the saw pretty much keeps paying for itself, but you also need to get down Well Prepared, Tetsuo Mori, and pay for some events (it's the only way you are getting clues), so he doesn't always have the resources he needs.
• The saw taking both hands means that, while Yorick is going to kill and kill and kill, he is going to collect approximately no clues unless the shrouds are very low. No Flashlight, Lantern, or Old Keyring for this guy! Well Prepared can help with this occasionally.
• Running a fighting deck with 2-3 weapons is an exercise in luck and nerves. Tetsuo Mori and Prepared for the Worst (or Backpack (2) can help find the saws, but they cost resources, which orick needs to get the saw into play or recover from misfortune. Vicious Blow and/or Brute Force can fill the gap a bit.
• You live in terror of any treachery that consumes Assets or prevents their play. Chainsaw Yorick without a Chainsaw only has some Shakespeare to fight the Mythos.

Kind of Useless Stuff

• Oops! is not as good as expected. With 6-7 attacks, Yorick doesn't miss that often, and, when he does, he often doesn't have 2 resources to spare. This can be mitigated a bit with Drawing Thin, but then you are including cards to include other cards, and you only have so much deck space. I suspect with Stella's lower combat (and better use of Drawing Thin), it might be more effective.
• Emergency Cache (3) looked very promising, but it actually has a slightly lower damage rate than Act of Desperation for reloading the saw, and it puts you in danger of Attacks of Opportunity. In a lot of TFA scenarios, Yorick is engaged with enemies pretty much constantly, so it's hard to find a moment to play Events.
• Relentless seemed promising, but, in TFA at least, there are a lot of 3 Health enemies to chop up, and you want to save the 2 Health enemies to fuel Act of Desperation, so you overkill less often that seems likely. After some fussing, there just wasn't a place for it in the deck. (Sorry DAAAN, I tried.)

It's not a terrible card; 2 icons and a "return to hand" effect is a nice hedge against failure, but I am not sure how often this will get played, given that 2 XP in will get you a Peter Sylvestre (2), "Look what I found!" (2), .18 Derringer (2), or 2 copies of Brute Force or Sharp Vision. I suppose Silas might like a situation where he contributes this and something else for, say, a +4 to a skill test, draws badly, then pulls the second card back with his Reaction Ability and this back with its own ability. That would feel pretty good.

If we consider a weakness' strength based on how many actions it takes to get rid of, Tommy Malloy is pretty harsh. His ability basically requires your team to spend three actions, minimum, to off him, which is more than most weaknesses.

There's also very few ways to mitigate the action sink, especially at level 0: you can use one-two punch to get 2 damage in one action, but you just played an event that normally does 4 damage for 2. The other option is Beat Cop, who you'd rather keep around as long as possible. Combine both and you can do it in one action, but you just spent six resources, static +1 combat, some soak and your most damaging event to remove a weakness. I'd rather just blow a whole turn taking basic fight actions, since Tommy's crummy fight stat makes him easy to hit.

In multiplayer someone could evade him, but solo that's really not an option. Even then, someone has to deal with him eventually, eating up your team's actions.

In short, he's really annoying, and will probably take three or more actions to get rid of. At least you can play Glory when you kill him.

AquaDrehz is right that this third version and Parallel Skids's spicy Deckbuilding Options allows you to bring 6 copies of Lucky! (2x each of level 0, 2, and 3) for 10xp. But why stop there?

19 Clove Gar-luck Chicken:

Let's take a closer look at his Additional Options. "When you upgrade a Fortune or Gambit card, you may instead pay the full experience cost on the higher level version and leave the lower level version in your deck (it does not count towards your deck size or the number of copies of that card in your deck)."

So, we start off with a couple of Lucky! (0), and we spend 2xp to upgrade one to Lucky! (2) and leave a special Lucky! (0*) that doesn't count towards size or copies. Now we pay 3xp and upgrade again to Lucky! (3) and leave a second special Lucky! (2*) in our deck. Awesome. Here's where things take a turn. We spend 1xp to buy a NEW Lucky! (0), replacing Lucky! (3). We have to replace it since we can't fit three honest Lucky!'s in our deck.

Now, hold up - buying a level 0 to replace a higher level version of itself, can we do that? Yup. It's already fairly standard practice if you want to change what Strange Solution you got (refer to its FAQ entry) after you got greedy and careless.

So we're currently at 2x Lucky! (0), 1x Lucky! (0*) and 1x Lucky! (2*). Special upgrade it two more times and you have 1x Lucky! (0), 2x Lucky! (0*), 2x Lucky! (2*), and 1x Lucky! (3), for a total of 11xp. Ever 6xp past this adds another Lucky! (0*) and Lucky! (2*). The sky is the limit in campaign mode, so lets use the Standalone Deckbuilding XP cap of 49. Spending 6xp at a time six more times, leaves us with 2 left over, which we can use to special upgrade that other level 0 that's been patiently sitting there. Final tally at 49xp:

• 9x Lucky! (0*)
• 8x Lucky! (2*)
• 1x Lucky! (2)
• 1x Lucky! (3)

For a grand total of 19 Lucky!'s of various levels. 17 of which don't count towards your deck size or card limit. Worth it? Probably not. Tasty? Definitely.

Lucky Number 13:

Realistically though, you probably don't want that many copies of Lucky! (0) in your deck unless you have enough other draw because it doesn't cycle, so maybe just stick to the stronger versions. We start with 2x Lucky! (0) (because why not?) and special upgrade them up to level 2 and then 3, but this time we purchase new level 2's to replace the 3's and do an abridged loop costing 5xp per loop.

• 2 Lucky! (0*)
• 9x Lucky! (2*)
• 2x Lucky! (3)

Much less chaff, an extra level 3, and 4 xp left over to maybe buy yourself something nice.

(You could also pull this trick to get 10 copies of Hot Streak or 19 copies of any other Fortune/Gambit with level 0/2 versions. "Look what I found!", A Chance Encounter, Daredevil, Dumb Luck, Oops!, or Daring Maneuver. Daredevil deserves special mention because you can use it to get +19 on any skill test and turn your deck into a pile of 6 weaknesses!)