While I won’t complain about getting something as a reward besides the achievement itself, I feel like just giving out units based on the achievements difficulty is kinda boring, I’m unsure if this is simply a “placeholder” reward for something else or if it is even feasible to change what achievements give you at this point, anyway, I think it would be a lot more interesting for achievements to give you something more long-term or exclusive, kinda like milestones, even the most difficult achievements give you 25,000 units, which can be earned in 2 games of Virus,Zombie Massacre or Ball Race.
Besides just cosmetics and other unlockables, maybe achievements could give you a small multiplier to your overall units earned? Similar to what some MMORPG’s do? Obviously, nothing crazy, having a 300% increase in units would be nuts, but something that benefits you in the longer term rather than just a lump sum of units.
I’ve heard that every 25,000 EXP in a gameworld will give you a unique catsack, which I think is a great idea, though, like my suggestion, I’d be worried how difficult it would be to give those benefits to older players who have 3,000,000 exp, perhaps the exp and achievement you earn could become points that you spend in some in-game store? Similar to the event tokens for Halloween and Winter.