Terrenials and the Trance gauge
When the Trance (TRC) gauge is full, the player has the ability to fuse with the current Terrenial. The 4 elemental Terrenials all have a special ability that make use of the Nintendo DS' features (i.e. touch screen and microphone). Toasty and Nero, however, are slightly different.
 Toasty with Aaron
- Solar Burst - Press the B button to let loose a ranged attack using the power of the sun.
- Solar Kick - Repeatedly tap the Y button to kick the enemy and absorb energy as well as deplete their life.
 Nero with Lucian
Nero fuses with Lucian to become a vampiric warrior. This form looks like a demonic version of Black Django. It has blue skin, black, blue and red hair and sharp claws. It also has vampire fangs (after all, what vampire wouldn't). This form also has 2 attacks.
- Dark Claw - Press the B button to let loose a long ranged scratch.
- Bloodsucker - Repeatedly tap the Y button to bite the enemy and drain the enemy's life.
 List of Terrenials
- Toasty - Terrenial of sol, restores energy upon use.
- Nero - Terrenial of dark, steals items/soll from a targeted enemy.
- Tove - Terrenial of earth, restores health upon use.
- Alexander - Terrenial of cloud, knocks back and stuns nearby enemies.
- Ursula - Terrenial of flame, attacks and stuns an enemy.
- Ezra - Terrenial of frost, freezes an enemy.
 Megaman Star Force and War Rock
Additionally, in the Japanese version of the game (i.e. Boktai DS), it was possible to crossover with the Japanese version of Megaman: Star Force (i.e. Shooting Star Rockman). After defeating the FM-ian Ox Fire, Aaron and Lucian gain a seventh terrenial, named War Rock. This feature was removed in Lunar Knights and Megaman Star Force.
- War Rock - Consumes nearby coins and transforms them into useful items.
Finally, Duke Dumas also has a dark terrenial named Perrault. Perrault is the boss in the space fight towards the Piledriver. Perrault controls the ship Schrödinger. Perrault is later revealed to be the other half of Nero, and despite its light appearance, Perrault appears to be the evil half. Whether these 2 were once Violet's cat Nero from Boktai 2: Solar Boy Django is unknown.
In the fight with Dumas, Perrault fuses with Dumas to become a very dangerous form of vampire, thirsty for blood and caring for nothing it knocks down in its way.