Colossal Serpent - It's magic attack is decent, but it can be defeated easily, and is very easy, just like most Orochis.
Elite Goblins - This battle is difficult because there are so many Goblins, but you can take their HP out easily. Also, they can make you angry, which can make the battle easier.
Heavy Golem - It has higher stats than the Goblins, and deals splash damage, so it's harder.
Neon Pharoahs - This one is annoying due to the Pharoahs' Curse, but fun fact - They only use that every odd-numbered turn, so just learn your team's attack pattern, abuse the safe spot and you'll not give any HP Bananas. They aren't that hard to take down otherwise.
Light Lord/Lighter Lord - These were obviously intended to be relief after the Red Fiend battle. The Light Sage has strong attacks, but the Light Lord is basically the Dark King with a few slightly buffed stats and a new look. Just safe spot abuse and have good stats and you'll be fine.
Burgers - These are really annoying as they eat your team, and leave one of them defenceless, so I recommend that if you're an Elf, put yourself in the safe spot at the start of the battle to prevent yourself getting eaten, then place a barrier over yourself until your team is spit out. Even then it's still difficult, as the Burgers will still keep eating you.
Boss Snurp - You might be surprised with the placing of this, as the Boss Snurp is the final boss and considered to be the most difficult, and yes, he is difficult. The Juvenile Snurps are hard, but just remember the order that they targeted you in, and you can prevent them from being reduced to 1 hp. However, the Boss Snurp himself has a strong attack, so that's a big challenge. I'd recommend protecting your healer at all costs, even from the start of the battle. Or if you're an Elf, place barriers, safe spot abuse, remember turn orders, and you'll be fine. However, there is one boss battle that is much harder than this.
Blue Godesses/Red Fiend - Yep, this is the hardest. The infamous Red Fiend battle. The Fiend can of course kill you in one turn, and the Blue Goddesses supporting it make it twice as hard. I'd recommend safe spotting your healer at the start of the battle to prevent them from getting killed, and when a team member's health is low, swap them out if it's the Godesses' turn. As for the Fiend, I'd recommend becoming an Elf to endlessly stun it with dancing arrow, and even then, the Godesses have strong attacks and can dip your heart into darkness, so the Fiend can still kill your team. Once the Fiend is defeated, place barriers over your team and start attacking the Godesses, and you'll be fine.
So that's my thoughts on the Tower of Despair bosses! What do you think are the hardest bosses? And what do you think about my list?