Overview
Riot has released their learnings blog for TFT Set 15: K.O. Coliseum, which features insights from their set lead, multiple designers, and art team folks. You can read their full thoughts here. And as always, you can catch latest comps and stats on our TFT page here.
Here's the TLDR on their thoughts:
Power Ups
Missed the mark
Too complex and inconsistent
Burden of knowledge (needing to know things that are not in the game's tooltips) was too high for the average player
Missing your Power Up felt much worse than hitting one that you wanted
Flexibility
Missed the mark
They'll aim to make traits feel more viable at lower breakpoints in the future
Artifacts
Missed the mark
Too much disparity between BiS artifacts and more general artifacts
Bugs
Missed the mark
Too many bugs -- they attribute it to trying too many new things
Monster Trainer
Missed the mark
Prismatic Traits
Missed the mark
Not entirely a loss but they're not going to make the "Quest" style of hitting them the default
Roles Revamped
Hit the mark
They are happy with the new roles and how champions gain mana now
Ao Shin's Ascent
Hit the mark
They are happy with the mode and feel like they've learned a lot -- no solid plans (that they're ready to announce) for any continuation as of yet though