How do I Create a good unlock success system?

Hi Guys, I Would like to know how can I create using an "organized" way to create a success unlock system...

Lets imagine that the player killed the first enemy, then the success "first enemy killed" must be unlocked...

I know how to do this.. but I don't think that my way is the best way because in my way I need to put all success sprites invisible on the hud (but it makes my project too desorganized)..

what is the easiest and good way to do a unlock success system?

The first time I created a achievement system like that I created a single object and set a different animation for each type of achievement unlocked.

Then you create a single invisible object on the screen and change it's animation every time it appears. It worked really well form me.

RayKi thank you so much ! good idea!