Guda Guda 3 CQ Breakdown

Breakdown:
The boss buffs itself with a bunch of defense buffs (3) in the beginning, so defense  ignoring NPs are recommended (otherwise it takes forever).
Every time the boss's break gauge (3 of them) breaks: one defense buff is removed, the class changes (from Archer-Assassin-Rider-Caster), debuffs are applied to your party (atk down, def down, stargen down -the amount of debuffs depends on which gauge # is broken-, and buffs self with critrate up, atk up and critdamage up (combination is different each time).
Their NP is AOE so plan accordingly.
Their skills include a critrate/critdamage up one and a NP charge one (1 tick).

My Party:
Level 10 Plugsuit
Mashu with 2030 CE, 10/10/10 NP3
Support Jeanne with MLB Prisma Cosmos, 10/10/10 NP5
Emiya (Assassin) with Another Ending, 4/4/4 NP2
Fujino with Before Awakening, 10/6/10 NP2
Andersen with Necromancy, 6/7/4 NP5
Ryouma with 2018 New Year's SSR Gacha Ce, 3/6/4 NP5

Strategy:
Build your NPs as fast as you can to whittle down the boss and protect your party from the boss.
Use your skills with your best judgement.
Switch your damage dealer to Ryouma on the last HP bar.
Do it right and a flawless victory is ensured.

Whale Options for this Setup:
Mashu: Waver, Merlin, Tamamo
Emiya (Assassin): Higher NP Level, Shuten, Kiara, Vlad III (risky)
Fujino: Higher NP lvl, Moriarty, Emiya or Alter (NP5), Ishtar???, Arjuna I guess
Andersen: same as Mashu
Ryouma (does double damage tho): Ozy, Medb (boss is female tho), Quetz

Budget Options for this Setup:
Emiya (Assassin): Shiki
Jeanne: Support Mashu, their other whale or budget stuff
Fujino: David, Robin, Euryale (boss is female tho), any other option with 2 Arts cards at least

CE Options:
Any CEs similar in effect to my setup

If you're unsure, the wiki is your friend.