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:
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.
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!)