Spellcard Strategy
One of the big parts of strategy in the game involves Spellcards. How you manage your spellcards dictates a lot about how well you can do in the dungeon.
Soaking
Soaking a Spellcard renders it useless. It recovers when the floor is changed, or by casting Sanae or Eirin. However, Soaking is a useful asset which allows Momizi to recycle her Spellcards that were attached. Cards can be removed from weaker equipment and transferred to better stuff, or simply cycled for more useful Cards. It's especially good when the helpfulness of a Spellcard has run out. For example, once Eirin is no longer a threat, you can remove the card from your Shield and have a nice emergency alternative. The traditional method employed to Soak attached cards is to use Nitori or Suwako, but the game provides a very convenient and cheap alternative: the water trap. While a hassle when you don't want it, if you find a perfect opportunity for a Soak, you can drop all of your Cards and equipment except the articles you need to remove cards from, and simply trigger the trap. Always check for this kind of trap before using up your Nitori and Suwako.
Emergency Cards
Spellcards have two uses, and the important thing to know is that there are two uses. At first glance, since attaching a Spellcard has a more permanent effect that can be reused, it seems that it's always better to reserve Spellcards for attaching good equipment (except for Suika, of course). However, it is wise to always weigh how useful a Spellcard can be for casting. Some really good emergency cards you may want to consider keeping on hand are the following.
- Reimu - Permanent Floor-wide Seal is incredibly powerful, especially against the likes of EX-Keine, Mokou, Eirin, Shinki, and Evil Eye Sigma. Also probably one of the best responses if you step into a Monster House. It allows you to get out safely and take your time to deal with the enemies.
- Lunasa - Since Slow is permanent on enemies, this makes a great alternative to Reimu when facing a Monster House. Not as disabling as Reimu, but it will save your life almost as well. Much less expensive than Reimu, as well.
- Letty - Not quite as good as the previous two, but better if you're simply surrounded. 10 turns of Sleep is too short to take out an entire Monster House.
- Kanako or Ran - Both are very cheap, and remove Momizi from danger. This merely prolongs the issue, but in some cases, careful repositioning is all that is necessary to survive. For the same reason, always keep at least one Warp Herb handy, if you can.
- Remilia - Remilia, Yumemi, and Mokou are the only characters immune to Flame Pillars. 20 damage doesn't seem like a lot late game, but wading through 5 of it in order to reach you is 100 damage, plus however much you can potshot for. If you have an entire room of enemies on your tail, lead them to a safe place and use this.
Status Immunity
A fair number of the Spellcards, on Shields, provide immunity to status ailments. This sounds great, but it is rather important to assess when it is great. For example, the Resonance Effect for Keine is "Level Drain Immunity". Sounds awesome and something you'd like for a long time, but the only way to lose levels is from Keine eating your history, which only occurs on floors 11-13. Keine on a Shield is great to have all the time, of course, but you needn't stick so closely to that sword except on those levels (unless you really need the Spellcard cost reduction). Furthermore, some of the immunities are double-edged swords. Eirin's effect prevents you from using HP recovery herbs, Lunasa's makes you unable to attain Haste, and Kanako's prevents you from warping by your own means. However, with any status immunity, but especially Eirin's, Momizi is able to eat otherwise dangerous herbs with no harm. This is also the only practical use of Paralysis immunity, which you can only self-inflict.
Other level-dependent status ailments are as follows. Blind is only from Mystia (7F-8F). Knockback/Warp from Meiling (6F-7F) or Kanako and Aya (24F-26F), Lunatic from Reisen (18F-20F), Curse/Soak from Hina (7F-8F) or Suwako (24F-26F). and Flame Pillar from Yumemi (19F-21F). Slow and Sleep always pose a threat due to traps.
Lyrica vs. Komachi
Blocking Sleep is very important, because 3 turns is all one enemy usually needs to mercilessly kill Momizi. And there will usually be more than one such enemy. Since traps can cause Sleep, they are a trouble no matter what floor Momizi is on. There are two ways to counter Sleep, Lyrica and Komachi.
Lyrica provides complete immunity to Sleep, plain and simple, so it sounds like the strictly better choice. However, Komachi can turn Sleep from a negative to a positive, due to the great amount of healing gotten. With Komachi, Sleep traps on the floor turn into healing spas. However, Momizi still loses at least 3 turns, which can put her in a dangerous position. It's up to preference, but in the late game, it is almost essential to have at least one of these.
Herb Synergy (Aya, Reisen, Meiling, Medicine)
Beyond the normal effects of herbs, there are (supposedly) 4 cards which provide great synergy with certain Herbs. These are the Resonance Effects of Aya, Reisen, and Meiling, and all effects of Medicine. They all provide incredibly powerful benefits, especially Meiling and Medicine, which can be stocked for later usage. The difficult matter is luck plays a lot more against these combinations than others. You need the luck to obtain both the Spellcards, and the Herbs. And since the effect is always temporary, you'll need a lot of Herbs, or need to reserve their usage carefully.
Attack Boost (Yuka, Hina, Medicine)
Three Cards will provide Momizi a significant boost in attack power: Yuka, Hina, and Medicine. Of the three, Hina is the most reliable as it can be carried from floor to floor, Medicine's is the most luck dependent due to requiring Poison, and Yuka's is in between, as it can be reliable called upon with good item usage but is utterly useless against Yukari. The boost in attack power is not something to scoff at. For example, upon reaching 28F, Momizi with a good sword can do roughly 50 damage to Evil Eye Sigma, for an average of 2 hit kills. With Hina on, this can be boosted to almost a guaranteed kill, while having Yuka always confirms a kill. With both, the damage is well over 150. As killing the enemy quickly is far more important than surviving more than 3 hits, the attack boost is extremely important. Do note that the damage boost is only for melee attacks.