How do I get Breedmarks to upgrade Habits?

Breedmarks are the second ingredient (alongside Cores) for leveling a dragon's Habits. Where the Core depends on rarity, the Breedmark depends on the breed: you need the Breedmark matching the breed of the dragon you want to upgrade.

Where to find them:

• Chests and events, notably Habit Growth, which is built around this system.
• The Market and the store (targeted offers).
• Campaign and leaderboard rewards.

A reminder on a Habit's cost: 1 Breedmark (breed) + 1 Core (rarity) per upgrade, to take each Habit from 1 to 5.

Strategy: since you need both items at once, check that you have a Breedmark AND a Core before you start, and concentrate them on the dragons whose 5th Habit (the strongest) is worth the cost.