Double Soul (MMBN4)

Double Soul (ソウルユニゾン Soul Unison) is the main transformation system of Mega Man Battle Network 4. To Double Soul, the player must sacrifice the respective element chip to unite with MegaMan. The transformation will last 3 turns or until it is overwritten by another Soul. However, there are Mod Cards that will allow MegaMan to remain in a Soul permanently.

• Normally Souls cannot access Dark Chips, but during ToyRobo's ShadeMan fight, the mandatory DarkSword will show up and can be used. It can also used to Double Soul into Proto Soul and be charged up.

Red Sun

Guts Soul
Sacrifice	Crack chip
Power Attack	Guts Punch (60 damage) Non-flashing. Small Push, pushes 1 panel.
Abilities	All Null and Crack chips gain +30 damage. Guts Machine Gun: Rapidly pressing B will make MegaMan temporarily invincible and execute a rapid fire attack. (10 damage, up to 5 times)
Fire Soul
Sacrifice	Fire chip
Power Attack	Flamethrower (50 damage) Fire attack.
Abilities	Fire Body: MegaMan can walk on Lava panels and is weak to Aqua attacks. Stepping on Lava Panel will have MegaMan consume it and heal 50 HP. Upon Unison, the stage is reset into one with plus-shaped Grass Panels. Charge Fire Chip: The chip becomes a Fire Arm that travels down the whole row. (Chip ATK + 50 damage)
Roll Soul
Sacrifice	Recovery chip
Power Attack	Roll Arrow (30 damage) The struck target's BattleChips are destroyed.
Abilities	MegaMan heals 10% of his HP anytime he uses a BattleChip.
Wind Soul
Sacrifice	Wind chip
Power Attack	Wind Racket (50 damage) Non-flashing. Big Push, pushes all the way down the row.
Abilities	B Button: MegaMan's normal buster becomes Air Shot. Air Shoes: MegaMan can walk over Broken panels. Float Shoes: MegaMan ignores Cracked, Ice, Lava, and Sand panels. Upon Unison, NorthWind takes effect. The enemy's Barrier or Aura are blown away. For 3 turns, a Fan effect is active on the enemy's field. The Fan effect can be overwritten by a Wind or Fan chip. If that obstacle is destroyed, there will be no Fan effect on the field.
Thunder Soul
Sacrifice	Elec chip
Power Attack	Zap Ring (20 damage) Elec attack. Paralyzes.
Abilities	Elec Body: MegaMan is weak to Wood attacks. All Null and Elec chips will paralyze. The paralyzation applies to all hits of a multi-hitting chip with the exception of ElemSand. Said chip will cause flashing regardless.
Search Soul
Sacrifice	Invisible chip
Power Attack	Scope Gun (10 damage x5) Pierces invisible.
Abilities	Upon Unison, all invisible enemies are no longer flashing. A Shuffle button appears on the Custom Screen that can shuffle non-selected chips with the Folder. This can be used up to 3 times per turn.

Blue Moon

Aqua Soul
Sacrifice	Aqua chip
Power Attack	Bubbler (20 damage) Aqua attack. Charges very quickly.
Abilities	Aqua Body: MegaMan won't slip on Ice panels and is weak to Elec attacks. Charge non-dimming Aqua Chip: x2 damage.
Number Soul
Sacrifice	Plus chip
Power Attack	Dice Bomb (10 damage x Die Roll) If the Die hits the enemy directly, it will only do 10 damage.
Abilities	All Null chips gain +10 damage. The Custom Screen displays 10 chips to select from.
Wood Soul
Sacrifice	Wood chip
Power Attack	Twister (20 damage, up to x8) Wood attack. Non-flashing.
Abilities	Wood Body: MegaMan will rapidly heal on panels and is weak to Fire attacks. Status Guard: MegaMan can't be paralyzed, blinded, confused, or immobilized. If a selected non-dimming Wood chip is followed by a Null Chip, the Wood chip consumes the Null Chip and its attack power is added to it. One of strongest Null chip target for Wood Soul's ability is BlueMoon. Through the Select Battle feature in Network, its attack power can be raised to 600.
Metal Soul
Sacrifice	Break chip
Power Attack	Metal Fist (150 damage) Breaking. Small Push, pushes 1 panel.
Abilities	Break Buster: The normal buster will pierce guards. Charge non-dimming Null or Break Chip: 2x damage.
Junk Soul
Sacrifice	Summon chip
Power Attack	Poltergeist (100 damage per obstacle) All obstacles thrown will be breaking.
Abilities	Upon Unison, all invisible enemies are no longer flashing and all enemies have confused status. Two recycled "Junk-Chips" appear in the Custom Screen every turn. The chips can be either from you or your opponent's.
Proto Soul
Sacrifice	Sword chip
Power Attack	Wide Sword (80 damage) Non-flashing. Unlike most busters, this attack can counter hit.
Abilities	All Sword attacks will not cause flashing. B + Left: Reflect. If an attack is blocked, 50 damage is sent down the row. Charge non-dimming Sword Chip: x2 the damage of the Sword Chip and MegaMan steps 2 steps forward while using it. Z Saver and Slasher BattleChips can be charged for x2 damage but MegaMan will not step forward. Unconventional Sword Chips will require more work. For VarSword and Z Saver commands, the A Button must be pressed down again after releasing it for the charge.

Glitches

• If 5 chips have already been selected in the Custom Screen but there still selectable chips; When the Unison is done with the last chip, the grayed out visuals for selectable chips are colored in again.