Guilty Gear XX Slash

Mission an character unlockables: 
Mission Artwork - Beat Mission Level 1 with the character. 
EX Characters - Beat Mission Level 2 with the character. 
SP Colors - Beat Mission Level 3 with the character. 
#Reload Characters - Beat arcade mode with the character. 
Order-Sol Mission Level 3 - Unlock Kliff and Justice. 

Unlock kliff: 
Beat survival mode level 400 

Unlock Justice: 
Beat survival mode level 420 

Unlocking other EX characters: 
Through survival mode,you can unlock EX and SP characters. 
After LV 500 youj will start fighting Gold characters instead of the EX ones in the order they appeared in EX forms. After unlocking the SP forms,Press start at the unlocked character then press right at the Directional stick. 

EX Order Sol - LV460 
EX A.B.A - LV480 
ES Sol - LV500

Guilty Gear XX Accent Core

Characters (EX):
To get the EX Characters, beat the Shadow version of them in Survival mode. To select them, hit Start on the select screen.

Ending Artwork (EX):
To get the EX ending artwork, complete Arcade mode with the corresponding EX Character.

Battle EX characters in Arcade mode:
Select the "Arcade mode" option, then hold L2 and hit Circle.

Battle Gold characters in Arcade mode:
Select the "Arcade mode" option; next, hold L1 and hit Circle.

Guilty Gear X2

Change Victory Pose:
Hold Punch, Kick, or Slash after the win message, but not everyone has a different pose.

Clean Pause:
Press SELECT while paused.
by - I-NO

Fight Skilled Opponents:
To fight only SP opponents, hold L1 for Arcade or M.O.M. mode. Holding L2 will force you to fight EX opponents, and holding both L1 and L2 will cause you to fight both versions.

Unlock Guilty Gear Mode:
Complete all 60 story mode paths to unlock the Guilty Gear Mode at the options screen.

Unlock Justice:
Beat Justice in level 230 in survival mode or complete all 60 story mode paths, or complete 40 missions, or accumulate 96 hours in training mode and normal game play.

Unlock Kliff:
Beat Kliff in level 220 in survival mode or complete all 60 story mode paths, or complete 40 missions, or accumulate 96 hours in training mode and normal game play.

Unlock Robo Ky:
Beat Robo Ky in level 210 in survival mode or complete all 60 story mode paths, or complete 40 missions, or accumulate 96 hours in training mode and normal game play.

Unlock SP Fighters:
Beating an SP character in survival mode lets you hold L1 when choosing that fighter on character selection to play as the SP version.
Or you can complete all three story mode paths to unlock the corresponding SP character of that fighter.
You can also beat 40 missions (50 for Kliff, Justice, and Robo Ky) to unlock the SP fighter costume.

EX Characters:
Once you beat a character in Survival Mode, you'll unlock its EX version. To select an EX character, highlight him/her, then press L2 at the character selection screen.

Stage Select:
To select a different stage, highlight a character and press R2. 

Guilty Gear X Plus

Alternate costume colors:
Enter "MJNKPNPN" as a password. Alternately, unlock all twenty four pictures in gallery mode. Hold Start when selecting a fighter to get a black costume with an unlimited gauge. Hold Triangle when selecting a fighter to get a gold costume.

New gallery mode challenge:
Enter "3GOU1SAD" as a password to unlock new gallery mode challenge.

Play as Dizzy and Testament and unlock GG mode:
Enter "KYUSBNBN" as a password to unlock Dizzy, Testament, and GG mode. Alternately, press Down, Right(2), Up, Start at the title screen. If you entered the code correctly, you will hear a sound.

Play as Justice:
Unlock eighteen pictures in gallery mode to unlock Justice.

Play as Kliff:
Unlock twelve pictures in gallery mode to unlock Kliff

Guilty Gear X

Unlock Extra Characters the Easy Way:
At the main title screen (where it says "Press Start") press DOWN, RIGHT, RIGHT, UP, START. This will unlock Testament and Dizzy.

Unlock Extra Characters the Hard Way:
To unlock Testament, beat the game in Arcade Mode or defeat Testament in Survival Mode. To unlock Dizzy, beat her in Survival Mode (level 30).

Unlock Guilty Gear Mode:
To unlock Guilty Gear Mode, beat level 100 in Survival Mode.

Guilty Gear Isuka

Unlock K.Ky And K.Sol: 
Score 1.4 million points in Boost Mode using Robo Ky 2 on normal difficulty. After clearing stage 5E (and beating Sol and Ky), stay away from the factory choice and fight Robo Ky 2 Substance. Defeat this opponent and the new characters can be selected by pressing START on Sol and Ky. (Unverified) 

Unlockable: Characters 

* Zako A for vs. mode: Beat boost mode 
* Zako B for vs. mode: Beat boost mode 
* Zako C for vs. mode: Beat boost mode 
* Leopaldon for vs. mode and in training: Beat him on level 200 in arcade mode 
* After getting 100 points in arcade mode EX mode characters start to challenge you. IF you beat them, they become playable. 

Unlockable: Antarctica Stage 
At level 100, defeat Leopaldan (arcade mode). 

Hint - Robo-Ky MK II Ultimate Special: 
This is the best special Robo-Ky MK II can use. To do it, you must have perfect timing between two specials. 

First, you must do Down + Forward + Forward + Square to do the "Limit Lovers" special, which has a countdown that starts from 9 and when reaches 0, Robo-Ky II gets shocked and hurts all players around him in the process. 

When the countdown reaches near the end of 4, then you must quickly tap Down + Forward + Forward + Triangle to do the "Whatever Is Done, a Fellow No Good Is No Good" special, which will take up the rest of the countdown time and reach to 0 when the special is finished. 

This means after the "Whatever Is Done, a Fellow No Good Is No Good" special, the big shock ball will immediately come around him and hurt players around, which ends up doing about 3/4 of one life bar, and up to a 46 hit combo!