For shits and giggles, I looked up what the "extremes" were, for monster attributes.
Most HP:
This guy, 6133 Max HP, 1363 Attack, but a whopping -500 (yes, NEGATIVE 500) RCU. Rofl. Ultimate evolution of Titan.
Max Attack:
This guy, Max HP 1581, Max Attack 1857, 226 RCU. he's not an evolution of anything, apparently you get him as a rare drop on highest difficulty in the Water Sky Dragon dungeon, no idea if that's out in NA.
Max RCU
This weirdo thingHP 400, Attack 800, Recovery 800. It looks odd, and it's the evolution of a drop that's in a dungeon that only came out in Japan in October, so I'm fairly confident it's not out yet here. Also, it's weird. (there were 2 more that had slightly higher RCU, but they appear to be upcoming, they had a reference to famitsu in them and no dungeon or gacha listed, so I think they're nto out in Japan yet. Also, they looked like Mickey mouse).
Highest Overall:
See Titan. Despite the -500 on RCU, he has the highest overall stat value with roughly 7k. but because he looks so badass, here's 2nd, with roughly 6k:
This badass 4.3k HP, 1.5k attack, 112 (lol) recovery.
That's it for today from "fun facts".
EDIT: and yes, the links lead to translated version. Why? Because that's the only way to use the Wiki, that's why. (aka I don't speak Chinese)