1. Floors:

Titan + Gemini Saga + Aries Mu

The Titan's SPD is still 600, Saga's is 435 and Mu's is 335. So, at the start of the battle, you'll be blasted by 2 AoEs, one from the Titan and one from Saga. The Titan will also revive dead Saints once its HP drops below 40%. Saga has enough energy to use his high-damage skill, and Mu will shield his teammate with the lowest HP.

2. Strategy:

As the clear conditions include having more than 40% HP remaining and as there is no way of avoiding the Titan's AoE, bringing a healer is recommended.

To deal with Saga and his 435 SPD, I recommend bringing Black Cultist as it has an initial SPD of 363 and equipping [New Moon] which gives 72 SPD, making it rather easy to act before Saga. It's worth noting that there are also Legendary Cosmo whose basic attribute is SPD!

If you control Saga for the entire fight, and just focus your attacks on the boss, all should be well. After all, one of the clear conditions is to defeat the Titan within 5 rounds, and that depends on your single-target damage dealers.

If you're worried about Mu's shields, you can take advantage of his mechanic of shielding his teammate with the least % HP remaining. Do so by keeping a monster with low HP alive so that he doesn't shield the Titan.