Ninja Class Djinni Combination
The Ninja Djinni combo is a Tri-Elemental class which is available to the Venus Adepts Isaac and Felix as well as the Mars Adepts Garet and Jenna in the first game. During Golden Sun: The Lost Age your Jupiter Adepts Ivan and Sheba will have access to this class combination as well.
Ninja is one of the best damage dealing Djinni combinations in the entire game and becomes available to your team fairly early on during the game. It has extremely powerful AoE abilities that dish out a ton of damage but have high PP consumption. Ninjas also get a few powerful single target abilities but primarily they focus on AoE damage.
If you're interested in becoming a Ninja on one of your Venus/Mars Adepts you'll want to follow my instructions below to make sure you use the appropriate Djinni combinations.
Venus Adepts: 3 Jupiter; 3 Mars (Ninja)
Venus Adepts: 4 Jupiter; 4 Mars (Disciple)
Venus Adepts: 5 Jupiter; 4 Mars (Master)
Mars Adepts: 3 Jupiter; 3 Venus (Ninja)
Mars Adepts: 4 Jupiter; 4 Venus (Disciple)
Mars Adepts: 5 Jupiter; 4 Venus (Master)
Jupiter Adepts: 6 Venus (Or 6 Mars) w/ 1 Venus/1 Mars
If you use 4 Djinni each instead of three you'll become a Disciple who has higher stat multipliers than a Ninja. 5 Jupiter Djinni and 4 Mars/Venus (depending on your adept) will give you the final version of the Ninja known as the Master which has even higher stat bonuses than the previous two.
During Golden Sun you will only be able to make one of the character's on your team into a Ninja/Disciple or Master. I very strongly recommend this class considering it has a lot of survivability and almost unmatched AoE & single target DPS.
Here are a list of all the abilities that the Ninja class will learn:
(Level 1) Gale: Hits 3 targets with 18 Power.
(Level 4) Punji: Hits 3 targets with 45 Power.
(Level 6) Fire Bomb: Hits 3 targets with 35 Power
(Level 7) Mist: Hits 3 targets
(Level 8) Thunderclap: Hits 3 targets with 50 Power.
(Level 12) Death Plunge: Hits 1 target with +40 Attack.
(Level 15) Punji Trap: Hits 3 targets with 85 Power.
(Level 16) Cluster Bomb: Hits 5 targets with 65 Power.
(Level 18) Typhoon: Hits 5 targets with 75 Power.
(Level 21) Shuriken: Hits 3 targets with Attack * 0.8
(Level 26) Thunderbolt: Hits 5 targets with 110 Power.
(Level 31) Annihilation: Hits 1 target with Attack * 1.5
(Level 36) Punji Strike: Hits 5 targets with 150 Power.
(Level 40) Carpet Bomb: Hits 7 targets with 130 Power.
(Level 44) Hurricane: Hits 5 targets with 150 Power.
(Level 50) Thunderhead: Hits 6 targets with 190 Power.
In conclusion, even though the Ninja specializes in AoE DPS I have still found the class extremely capable of dealing a huge amount of single target DPS during encounters with only a single enemy. With the high Agility, HP & defensive capabilities mixed in with the spectacular DPS a Ninja can do it's difficult to find a reason not to have this class on your team.