According to these lovely fansites there's 26 achievements points in total when unlocking creatures in the Bestiary. Here's a list of achievements and their descriptions with the points.
Contender 3 points - Obtainable by unlocking 10 medium monsters in the Cyclopedia.
Hunting Permit 3 points - Obtainable by fully unlocking any monster in the Cyclopedia.
Little Adventurer 3 points - Obtainable by unlocking 10 easy monsters in the Cyclopedia.
Little Big Adventurer 2 points - Obtainable by unlocking 100 easy monsters in the Cyclopedia.
Master Hunter 6 points - Obtainable by unlocking 100 hard monsters in the Cyclopedia.
Serious Contender 4 points - Obtainable by unlocking 100 medium monsters in the Cyclopedia.
Skilled Hunter 5 points - Obtainable by unlocking 10 hard monsters in the Cyclopedia.
Sources:
https://guildstats.eu/ach-checker?s=1&lang=en
https://tibia.fandom.com/wiki/Achievements