Kinda surprised this wasn’t added in alongside the other 1.4.4. Achievements but there should be an Achievement for filling out the bestiary to 100% in a world. This would obviously fit in alongside the other more difficult Achievements and shouldn’t be too hard to implement.
Also small little nitpick, currently the Achievements are in the order they were added to the game. I think it would make more sense to put them roughly in order of progression or objective difficulty.