How do you upgrade a dragon's Habits (Breedmark and Core cost)?

Upgrading a Habit costs two materials at once:

• 1 Breedmark matching the dragon's breed
• 1 Core matching the dragon's rarity (🔵 Rare, 🟣 Epic, 🟡 Legendary)

The life of a Habit: locked → unlocked (lvl 1) → raised to lvl 5. Every dragon has 5 Habits, each over 5 levels.

An important nuance: Star Rank unlocks the slots, but Breedmarks + Cores are what raise them from 1 to 5. That's why a dragon can sit on plenty of stars with low Habits — you simply ran out of materials.

There is a Habit Growth event: upgrading Habits scores points there, and higher-rarity dragons score more — with each dragon's 5th Habit the most valuable of all.