In Ultimate Battle Z mode on difficulty level 3 there are hidden battles that need specific conditions to unlock. Complete the following tasks to unlock the corresponding battle.

Fight Brolly Legendary SSJ in Saiyan Blood:
Using an Ultimate Blast defeat Bardock.

Fight Goku SSJ2 and Vegeta (2nd Form) SSJ2 in Dragon Tag 2:
Using an Ultimate Blast defeat any opponent.

Battle Hercule in Unlimited:
Defeat Gogeta SSJ4

Battle Super Baby 2 in Normal-ism:
Using an Ultimate Blast defeat Super 13.

Battle Uub in Kakarot Road:
Using an Ultimate Blast defeat Kid Buu.

Battle Omega Shenron in Ultimate Dragon:
Using an Ultimate Blast defeat Syn Shenron.

Battle SSJ3 Gotenks in Ultimate Children:
Using an Ultimate Blast defeat Kid Goku.

Battle Tao Pai Pai in Assault Force:
Using an Ultimate Blast defeat any opponent.

Complete the following tasks playing through Ultimate Battle Z mode to unlock 6 extra secret characters which are only available in the European, Australian and Japanese versions.

Unlock Frieza Soldier:
Complete Course 2.

Unlock Appule:
Complete Course 4.

Unlock Cyborg Tao:
Complete Course 6.

Unlock Demon King Piccolo:
Complete Course 8.

Unlock Pilaf Machine:
Complete Course 10.

Unlock Pilaf Machine Combined:
Complete Course 10.

To get Bra instead of Bulma at the 'Start' screen of Training Mode complete ALL of the Basic Training.

Enter the following combinations to unlock the corresponding character.

Unlock Android 13:
Computer + Hatred

Unlock Android 13:
Fusion Android 13 + Parts of 14 & 15

Unlock Bojack:
Unsealed + Galactic Warrior

Unlock Broly:
Son of Paragus + Hatred of Goku

Unlock Cooler:
Frieza's Brother + Hatred of Goku

Unlock Cooler Final Form:
Super Transformation + Cooler

Unlock Cui:
Vegeta's Rival + Frieza's Soldier

Unlock General Tao:
Bros. Of Crane Hermit + Memorial Campaign

Unlock Great Ape Bardock:
Power Ball + Bardock

Unlock Great Ape Nappa:
Power Ball + Nappa

Unlock Great Ape Raditz:
Power Ball + Raditz

Unlock Great Ape Turles:
Power Ball + Turles

Unlock Great Ape Vegeta:
Power Ball + Vegeta (Scouter)

Unlock Hirudegarn:
Hirudegarn's Top Half + Hirudegarn's Lower Half

Unlock Janemba:
Saike Demon + People's Bad Energy

Unlock Legenday Super Saiyan:
Broly Super Saiyan Broly + Breakthrough the Limit

Unlock Metal Cooler:
Big Gete Star + Cooler

Unlock Salza:
Coolers Soldier + Armored Cavalry

Unlock Super Android 17:
HFIL Fighter 17 + Android 17

Unlock Super Saiyan Broly:
Broly + Super Saiyan

Unlock Zarbon Post-Transformation:
Unsealed + Zarbon