I manage to get these information by inferring from Guardian Cross (GC) Jp Wiki link as well as these threads (1, 2) from guardiancross-forum.com for help in the names. I'll put the shapes first as these will help in hunting.
Update(09/10/2012): Added skills translated from Guardian Cross (GC) Jp Wiki link and my comments. I will try to talk more about the Guardians' stats here unlike the 3* guardians that I did earlier.
5*
Machine
Gargantua
Shape: Floater
Skills:
Level 1: Cross Slash (physical+2)
Level 15: Heavy Blow (physical+2)
Level 30: Hard Slash (physical+3)
Level 40: Double Impact (physical+3)
Level 50: Storm Impact (physical+4)
Comments: Strong physical attacker with high attack and defence. The skill choices aren't too hard to make: Skill 3, 4 and 5.
Water
Apsara
Shape: Humanoid
Skills:
Level 1: Aqua Slash (water+1)
Level 15: Aqua Shot (water+2)
Level 30: Greater Haste (agility+20%)
Level 40: Mind Blast (wisdom-20%)
Level 50: Maelstrom (water+4)
Comments: From the stats, this look like a fast elemental attacker. It comes with its own wisdom debuff to benefit immediately by dealing more damage with its water attacks. Note that the debuff does not trigger for the next guardian opponent. The last 3 skills are the best.
Undead
Frankenstien
Shape: Giant
Skills:
Level 1: Heavy Blow (physical+2)
Level 15: Thunder Strike (lightning+2)
Level 30: Double Impact (physical+3)
Level 40: Call Lightning (lightning+3)
Level 50: Storm Impact (physical+4)
Comments: High HP, attack and defence. I think he is a physical attacker but he gets lightning abilities as well. The best 3 skills should be the best unless you get a powerful one, which you probably should choose all the physical attack moves. I read some people comparing it to Titan but Titan's moves include buffs which, in my opinion, makes it stronger.
Poison
Azi Dahaka
Shape: Wolf
Skills:
Level 1: Poison Mist (poison+2)
Level 15: Poison Field (poison+3)
Level 30: Slow (agility-20%)
Level 40: Mind Blast (wisdom-20%)
Level 50: Venom Riot (poison+4)
Comments: This is similar to Apsara, with 2 debuffs instead. The HP, attack and wisdom stats are high. I think it will probably work best near or at the end of the team as the debuffs only work on the first guardian, following which, it will be left with a Poison+4 attack for the remaining of the match. Last 3 skills are the best.
4*
Wind
Qiong-Ji
Shape: Giant
Skills:
Level 1: Wind Cutter (wind+1)
Level 15: Haste (agility+10%)
Level 30: Wind Edge (wind+2)
Level 40: Slow (agility-20%)
Level 50: Greater Haste (agility+20%)
Comments: This guardian is strong in attack and agility. It desperately needs a physical+3 attack to replace Skill 3. Otherwise, it will be stuck with the last 3 skills.
Death
Revenant
Shape: Floater
Skills:
Level 1: Darkness (darkness+1)
Level 15: Hard Blow (physical+1)
Level 30: Dark Pain (darkness+2)
Level 40: Heavy Blow (physical+2)
Level 50: Dark Psalm (darkness+3)
Comments: It has high attack, defence and wisdom. I find the artwork very cool. The last 3 skills are recommended.
3*
Undead
Grim Reaper
Shape: Floater
Skills:
Level 1: Darkness (darkness+1)
Level 15: Dark Pain (darkness+2)
Level 30: Slow (agility-20%)
Level 40: Mind Blast (wisdom-20%)
Level 50: Dark Psalm (darkness+3)
Comments: It has high attack and wisdom and can be use as a debuffer like Nue. The biggest difference is that it has a +3 attack skill which can deal quite an amount of damage. Skills 3,4 and 5 are the best.
Fire
Surtr
Shape: Giant
Skills:
Level 1: Burning Beat (fire+1)
Level 15: Hard Blow (physical+1)
Level 30: Burning Strike (fire+2)
Level 40: Heavy Blow (physical+2)
Level 50: Explosion (fire+3)
Comments: It has high HP, attack and defence. The last 3 skills are the best.
2*
Light
Scarab
Shape: Bird
Skills:
Level 1: Holy Light (light+1)
Level 15: ?
Level 30: ?
Level 40: ?
Level 50: ?
Comments: Not enough information.
Dark
Ammit
Shape: Wolf
Skills:
Level 1: Darkness (darkness+1)
Level 15: ?
Level 30: ?
Level 40: ?
Level 50: ?
Comments: Not enough information.
iTunes App Store link: Guardian Cross - SQUARE ENIX
