The heart gauge is used to measure how closed the heart of a Shadow Pokémon is. The gauge is split into five major sections. As the Pokémon opens its heart to the player, the bar starts to decrease, revealing a white background. When the Pokémon has opened its heart to a major level, it will obtain one of the following:
- Checkable Nature
- Regained move(s)
- Ability to earn experience and gain effort points which are applied after purification.
The heart gauge is affected by several factors, such as:
- Being in the player's Party
- Using scents
- Battling with the Pokémon
- Being placed in the Purification Chamber (Pokémon XD only)
When the value of the gauge reaches 0, it will glow and is ready for purification. After being purified, the Pokémon becomes a normal Pokémon and gains a ribbon. All experience gained through battles as a Shadow Pokémon will also be awarded.
The Lugia factor
In Pokémon XD: Gale of Darkness, XD001's heart gauge is fully closed until it is placed in the Purification Chamber with all nine chambers being at max tempo. The heart gauge will automatically open and XD001 can be purified. However, if Lugia is taken out before being purified, then Lugia's Heart Gauge will close completely.