Gamble! should mainly be used when Yuki is low so that she can use it to KO herself and be able to revive at full HP. However, the card also comes in handy for certain niche scenarios, like removing Krilalaris' overheal, shutting down Miusaki after she activates Solid Witch, disabling expire-on-KO effects (most notably, reverting the transformation to Sweet Eater), and as a desperate way to KO someone in the lead to stall the game and give Yuki a potential chance of winning. Even with that said, it is inherently inconsistent in these other scenarios, as it can just as easily backfire by setting Yuki back several turns or giving a low HP enemy a free reset.
Mimic can be a very useful card as it can supply Yuki with stronger hyper cards from other players. Under the right circumstances, the card can make Yuki a much deadlier and unpredictable opponent. However, it makes dealing with everyone else a lot scarier for Yuki as it allows them to also gain more powerful hypers to use against her.
Sink or Swim can allow Yuki to gain much more stars from a KO against a low HP target while the stat nerf doesn't matter as much since she will have 1 ATK for still reliable KO's. However, this card can also be used against her reliably when she is at 1 HP since she only has -1 EVD.
Desperate Modification is a good defensive card for Yuki since it increases her chances of survival against 1 ATK when she's at 3 HP or lower, and against 2 ATK when she's at 4 HP or lower. What makes it truly good on Yuki is the fact that it doesn't protect against her well, and it makes unlikely KO's more likely to happen as well.
Final Battle can be really good for Yuki since the only characters she loses to on average if she goes first are Tequila, Store Manager, Sherry, Islay, and Maltif they are at full HP, so she can play it relatively safely for a KO that she desperately needs.
Gift Exchange and Scrambled Eve allow Yuki to easily disrupt card usage while not being affected by it as much since her amazing stat line makes her not reliant on cards.
Lucky Sevens fulfills multiple roles for Yuki. The main thing is that it gives Yuki more power on average, especially the chance to KO in one hit. This power increase allows Yuki to beat Sherry on average when they are both at full HP. To add to this, it can be a lifesaver at low HP due to its marginal boost to evasion prowess when defending is not a realistic option, giving her a 31.25% chance to evade against neutral ATK at 1 HP as opposed to 27.78%. She doesn't have to rely on having it herself to achieve the bonus power since she gets the same rolls on average against someone else holding Lucky Sevens. It also allows her to recover faster on average, but this isn't as important as it is on Tomomo. The 7 roll can also allow Yuki to reach a target that would have otherwise been impossible to reach, however she is less likely to be able to roll onto opponents while holding onto it on average; turning the 58.33% chance to fight them the next turn into a 56.25% chance.
Unsurprisingly, as the card art depicts her, Tragedy in the Dead of Night can be a lifesaver for Yuki when being attacked at 1 HP - increasing her chance of getting a life-saving card from 0% to >0%, just as a point of reference, and due to its double-edged effect, can also help her snipe enemies at low HP without having to use her Hyper.
Shield, Tactical Retreat, and Shield Counter can be effective against Yuki, as they can either reduce or prevent her from dealing damage. They also prevent her from using them aggressively for a safe fight since they must be used when defending. Shield Counter is the best one against her since it guarantees escaping from her, and it will deal 3 damage to her to either scare her off of fighting for a while, or KO her and force her to wait out her 5 REC. However, it is best to avoid using it when she is at 3 HP or lower if at all possible so that she doesn't revive at full HP while keeping all of her stars. However, Shield Counter and Tactical Retreat can also be really good on Yuki herself, since she can use them to avoid near certain death when at 1 HP.
Dinner can be used to prevent Yuki from KOing her target, or force her to heal everyone else when she wants to heal, which makes her 2 ATK less oppressive.
Out of combat damage cards like Long-Distance Shot and Cloud of Seagulls can be devastating to Yuki since she has -1 EVD, however, she can also use them to become a much scarier threat than she already is.
Oh My Friend can be brutal against Yuki, as it can stop her from gaining stars from encounter panels, and also makes it likely for her to die if she steps on a boss panel. It can also easily put a stop to her if she decided to go for wins norma.
Pet Snacks similarly makes it harder for Yuki to gain stars from encounter panels while increasing the chance that she takes a serious hit.
Play of the Gods can be used whenever someone is low for a chance for it to pull Gamble! from Yuki's hand and allow them to reset to full HP.