Achievements for goals would give you bows, the first one unlocking at 100 goals and then exponentially higher.

Achievements for demos would give you different suits, I like the idea of the highest one just being the exact same shade of red as the ball when it can demo you. First one unlocks at ~15 demos.

Achievements for blocks (amount of times the ball has touched your blocks)

Would of course yield blocks.

For all of this to work it obviously shouldn't be possible to unlock in custom games and imo it should only be from competitive.

The highest rewards should also almost be ridiculously high so that it will take a long time for people to get to them, and you don't have to keep adding new stuff that looks "cooler and cooler", I think that'd take out the value of the actual end achievements.

So for goals the end achievement would maybe be at 100k+ goals.