The border on certain levels mean that it is the maximum level for that league (league level is represented by border color).
In the screenshot for example:
- Level 3 - Bronze border
- Level 5 - Silver border
- Level 8 - Gold border
Because these are the max levels of disintegrator that you can play in Bronze, Silver, and Gold league respectively.
Wow! Thanks for a great explanation @peakmonsters . Now that I know, it seems pretty intuitive. @reverio Thanks for the system that allows people to learn! @hiro.juegos and @thebighigg here's the official answer from Peakmonsters.
I'm glad you asked, know we all know!
Keep the questions coming!!
Thanks for tagging them! :)