Milestones

Milestones are goals that rewards the player items or gifts, when they achieve the goal. 

Pet Milestones
Pet Milestones are milestones that reward the player Pets when they achieve them.

Dolphin Pet :

It is obtained by killing Sea Creatures.

The milestones are as follows;

Rock Pet :

it is obtained by mining Ores. Stone, Cobblestone, Endstone does not count.

The milestones are as follows;

Dungeon Milestones
Dungeon Milestones are class goals that give the player the possibility to gain better loot and to earn more class XP after clearing a Dungeon.

The Milestones vary for each class and are greater on higher floors;

Achieving Milestone 2 is required to open the Post-Boss Dungeon Chest,you'll also get reduced Catacombs and Class Experience if you fail to reach Milestone 3 before the dungeon run ends.

Other Milestones
The Enchantment uses the milestone system to upgrade.

It is upgraded by killing Sea Creatures while having the Expertise enchantment on your rod.

The milestones are as follows;

Trivia

 * While players cannot see their Milestones progress, their progress can be retrieved from SkyBlock API.
 * Fishing rods that have been enchanted with store expertise_kills in their NBT data.
 * You can easily look your progress up on sky.shiiyu.moe, which is a stats tracker.