Jack of All Trades (15)
Complete at least one challenge for every instrument at Gold level or better

This is meant for 4 instruments, Band challenges are not needed.

The challenge rewards are Gold, Platinum, Diamond, so Gold is actually pretty easy to get, a lot of them can be obtained on easy.

So you don't need to be able to do great, or get good scores, you just need to be able to hit 3-4 phase.s