Not meant to be "SPOILER" so read with a little caution if you're just about to do UNCOLLECTED Event
Just COMPLETED the UNCOLLECTED Monthly Event and here's my initial thoughts:
First a little about my game progression. 1 yr 3 months. 340K with 9 R5 4*s, 1 R4 5* (Magik duped), and 1 R3 5*, 20 R4 4*s.
Team used: 5* Magik, 4* R5 AA duped, 4* R5 Vision AoU duped, 4* R5 Ultron duped, 4* R5 IceMan duped.
Fighting ability: Slightly above Average (nowhere close to boss killer but can occasionally take out mini bosses in AQ)
Notable Events done: RoL (just last week), Boss Rush, Goldblum, RTTL Chapter 4 Round 2, Uncollected just a month ago
If you have at least 5 x R5 4*s (or better) everything is a breeze until Chapter 3 (Please Come Again) Last Resort. Nodes are just long fights, and try not to die.
So I felt it was going to be Collector level difficulty (Act 5.2.5 - Act 5.2.6) and it was actually a bit easier.
Things changed when I got to Ice Phoenix. I KOd Collector with just 10 L2 Revives with 5* Magik. Ice Phoenix is like Collector x 5 difficulty. Strangely enough, I thought my 5* Magik was going to be my best champ against Ice Phoenix but she wasn't. It was my 4* R5 Vision that did at least 30% of the damage when I include the total damage of the rest of my champs. I recommend watching YouTube videos on how to take her out before going in. It was just a brutal fight, altogether, and reminded me of what it was like fighting Maestro in Chapter 4 using an R4 4* and have no idea how to fight him. But Ice Phoenix is probably Maestro x 15 or 20 difficulty. (used 10 full Level 2 Team Revives on this fight alone)
The Task Master after Ice Phoenix wasn't too bad. Fight with skill and you can take him out without revives. Task Master is much much easier than Ice Phoenix. Again Vision was the most useful champ against him.
Hot Stone Massage had some difficult nodes but everything is skill until you get to MODOK. I think he's around 20-30% more difficult than Collector. Great fighting skills will help you with MODOK unlike with Ice Phoenix, so with my slightly above average fighting skills I took MODOK out with less than 3 full L2 team revives.
I spent a total of 1500 units to COMPLETE Uncollected Monthly difficulty. 1000 units on Ice Phoenix fights, 300 on MODOK and 200 on some other nodes I became careless.
I know it was unit galore for my first try so hopefully in the next few weeks I can get better. It's not impossible. It's just that Ice Phoenix fight was really crazy.
Good luck and I hope you spend less than I did.