There are 3 levels of progress when unlocking the bosstiary.
> Unlocking these levels you get rewards
> These levels depend on how often bosses can be killed.
1. Prowess Level
Reward: Boss Slot
> Unlock this level and get the first boss slot
> Select a boss and benefit from a 25% equipment drop bonus
> This bonus only affects equippable items
2. Expertise Level
Reward: Podium of Vigor
> Unlock this level and get a free boss display podium that can be placed in your house or GH
> You can purchase extra pods for gold
3. Mastery Level
Reward: Additional 25% Equipment Drop Bonus
> Completing Boss Entries will earn you "Boss Points"
> Boss slot equipment loot bonus can be gradually increased up to 182%
> You will earn a second boss slot upon completing 1500 boss points
> Progressing in the Bosstiary will grant temporary and permanent titles
> New record "Boss Points" will be added
Source: news summary June 17, 2022 tibia official website