There are so-called illegal parts that can be used in the game. In order to gain access to these parts, you must obtain the Majel Set, the Dark Commander Mark and have completed your doppelganger in battle. Once that’s all done, you’ll be able to access the Underground to buy your illegal parts. To get to the proper area of the Underground, head forward from the entrance and enter the door. Now, head to the right and go straight again. You’ll come across the illegal parts shop. Note: Robos excludes the Ray 01 and Ray Sky types. Costs are as follows:
Unlock the following fighters by performing the corresponding tasks in Grudge Match:
FIGHTER - HOW TO UNLOCK Cleaver - Get 20 illegal parts. Eddy - Win all other grudge matches except for Liv. Hardoron - Defeat the four Greybaum boss data. Kindaj - Get10 illegal parts. Liv - Defeat Eddy. Marv - Complete level 10 in the arcade (just the Robo). Marv's parrot - Get 7 gold trophies in the arcade. Sling - Get 15 illegal parts. Stark - Get "Marquises" rank. Sythe - Use 20 illegal parts. Yourself (first time) - Win 10 to 13 grudge matches. Yourself (second time) - Defeat Hadron.
To access a secret passage to The Underground stage, win twelve Grudge matches, then go in front of the clubhouse and defeat your shadow self to get illegal parts and the Dark Commander Mark. Then, talk to the suspicious man in the southwest house in the Bayside area.
To shrink the Amun gun and Amun bomb parts to the size of a normal gun, at the end of the game, after purchasing the Pipit Robo, the Jameson Robo, and all Amun parts, equip the Amun parts to Jameson, then Pipit, then Jameson again.
To unlock the following Robos, first complete the Great Robo Cup. Afterward, perform the corresponding tasks:
ROBO - HOW TO UNLOCK AIRS - Defeat Stark twice in the grudge matches. Carat - Beat all the Robo type Mission battles, then defeat Catoreya. Hadoron - Beat all four Greyham Boss data and Hadoron data to unlock Hadoron and his parts. Hiykko - Go to Team No. 1's Clubhouse and talk to the boxes above the stairs. Defeat the kid that is hiding inside the box without having a combo over 380 damage. Meijel, Nanase set and key to the Underground - Defeat your shadow self aboveground. Minstrel - Defeat Hajime in your classroom after he brings Saki to school. Ray and Sagittarius Gun - Defeat Saki in your classroom after she returns. Ray MK II - Go to your father and older sister's lab and talk to your father. Ray II Dark Robo - Defeat your shadow self in the underground for the second time. X-Ray - Go to the police station, and talk to the person behind the back desk without a microwave to purchase the Robo for $500 credits.
After completing twelve grudge matches, a doppelganger of your character will appear in front of your team's clubhouse, appearing almost exactly like your main character. You'll be forced to fight him. Defeat him the first time to get the Majel Robo, the Indigo Gun, Indigo Bomb, Indigo Pod, and Indigo Legs, as well as a pass that allows you to access the underground. After defeating the Greybaum enemies with the boss data, you can again fight the doppelganger. This time, he will give you the Ray II Dark Robo, Ripple Laser Gun, Deva Bomb, Cerberus Pod, and Phantom Legs.