every achievement should give you a cosmetic. here are some quick cosmetic ideas and their corresponding achievements.
You shall not pass!: wizard hat for scary neighbor
Sherlock: sherlock hat for detective
No Crows Allowed: something for guest
First one!: track gear for leader.
#achievement cosmetics
winged blade
feral briar
probably shouldn't be every achievement but yeah i like it
jaunty wing
Would be cool, hope they add more achievements though