This is a long post, so that's there. I'm just going to rank the three ItF bosses based on how fun they are, how difficult they are, their appearance, progression timeline, all that.
3. Cli-One
This may come off as cliche, but Cli-One is the "worst" boss of ItF. It's not a bad boss at all, no it's not. I'm only saying "worst" relative to the other 2 bosses. It's a good introduction to tough alien bosses, and seeing as most players begin ItF as soon as they finish EoC chapter 3, from a progression standpoint, the low difficulty makes sense. However, it just doesn't quite set the stage for the difficulty of corrupted valkyrie and raging bahamut. I do like the sea angel design, as they already look like aliens in our waters, so that design added with the alien trait, I just see that fitting.
2. Raging Bahamut
The final boss of ItF, and it really delivers, but not my favorite ItF boss. When you fight him, he'll have the raw stats of 1,222,222 million health, but a staggering 44,444 damage per hit. Keep in mind, he attacks every 1.17 seconds, has area attack, and stands at 320 range. The peons are also buffed very high even with all anti-unstarred alien treasures. It's a boss meant to test your mettle, and I really think it does a great job at doing so. It makes sure you are keeping your meatshields at all times, and cycling your main attackers for the peon waves, mainly the LeMurrs and Ursamajors. The LeMurrs also have weaken, which can make taking them out take even longer, and you'll have even less time to prepare for the next wave, just like in Forest Beasts, or Draconian. Overall, as the final boss of ItF as a whole, I really respect it, and it truly does test your mettle, and prepare you for CotC. Raging Bahamuts design is a great design, seeing as it's just like corrupted valkyries- it's one of your units, but upgraded. Going into specifics, I'm not the biggest fan of draconic designs, but Raging Bahamut has the world-ending draconic monster design done well.
Corrupted Valkyrie
As the final boss of ItF chapter 2, I believe Corrupted Valkyrie is the best boss in ItF. At your progression point when you fight her, her stats will be a monstrous 1.5 million hp, 21k per attack, 350 range, she attacks every 1.97 seconds, and has area attack. Surprisingly, I find this boss to be harder than raging bahamut, for a couple reasons. First, you fight her much earlier on, and the difficulty of ItF 2 stages compared to ItF 3 stages is a huge difficulty spike to say the absolute least. You'll have around one or two crazed cats, compared to raging bahamut, when you'll most likely have every crazed cat, even if you only use four of them. Corrupted Valkyrie tests your mettle just like raging bahamut, only it's like giving a 5th grader a calculus test. You'll be replaying the ItF moon 2 over and over, trying to find the best strategy. Whether it's cycling legends to constantly have large damage, using 5 meatshields and using long ranged attackers, or playing the long game and using low damage high utility CC cats like cyberpunk, which I doubt you'd even have by the time you get to ItF moon 2. Her design as a Valkyrie is immaculate, looking just like your unit, but upgraded. The flowing dress really makes her seem angelic, but her alien trait could make her seem unholy aswell. Overall, in my opinion, Corrupted Valkyrie is the best boss in ItF.
Well, thank you for reading this list. Now if you disagree with anything, which I guarantee you will, comment your opinion down below!