Challenge 1: Healing Rumi will allow her to heal her ally and help you in battle. Normal HG enemies can drop a shield that will block all damage for a short duration. Normal MG enemy will have a gauge next to her HP, and you need to apply CC (around 5s) to fill it up; otherwise, the Normal HG enemy will not take any damage.
Challenge 3: There aren't really any gimmicks in this one. Mina's HP is really high, so killing Kokona first is recommended. You might also want to reposition your tank forward to avoid Saya AoE poison since your DPS will be in range if not. You can probably skip most of the tip by having a giga-buff Iori.
Challenge 5: This stage is stupidly hard, so if you're underleveled or missing a lot of units, you will struggle to do the challenge mission (90s clear) in time. There's a gimmick where you will have ally mobs helping, and whenever they attack, they will apply Damage Taken UP to the enemy, allowing you to kill them significantly easier. As such, it is important to keep as many of them alive as possible. Koharu, Iori, Hoshino (Swimsuit), Ako, and Himari are essential for the challenge mission.
A set of 4 cards will be presented to the players. Revealing the first card will cost 200Card set, and the price will increase by 10 for any subsequent card after it (200, 210, 220, and finally 230); player can reset the hand at any point instead of revealing the next card, resetting the cost.
There are 4 rarities that can appear in the event card: SSR / Ultra Rare (Rainbow Border), Super Rare (Golden Border), Rare (Blue Border), and Normal (Gray Border).
Each set of 4 cards has a minimum of one SR or better card.
All 4 cards are random and a set might not contain an UR card.
Regardless of rarity, each card will always contain Solvent Extraction Set which is required to exchange items from the 3rd Shop.
Similar rarities will contain mostly the same rewards but at different quantities.