Advance Wars/COs

Andy
Andy has all-around average units.
 * CO Power: "Hyper Repair", increases all units' HP up by 2.
 * Unlocked by: Default

Max
Max is a direct fire specialist, all of his direct fire units get a 50% offensive bonus. Max's indirect units get a 10% offensive reduction, and one less square in their range.
 * CO Power: "Max Power", direct fire units get 25% offensive bonus and 1 extra square of movement.
 * Unlocked by: Default

Sami
Sami is an infantry specialist, all infantry units (infantry and mech) get a 20% offensive bonus and a 10% defensive bonus. Sami's troops capture buildings at 150% speed.
 * CO Power: "Double Time", infantry units get 30% offensive bonus, 20% defensive bonus, and 1 extra square of movement and lack moving penalties for that turn.
 * Unlocked by: Default

Nell
Nell's units have a higher luck rating than the other CO's, being able to do more damage than normal at random.
 * CO Power: "Lucky Star", All of her units gain a much higher luck stat, being able to do a much higher amount of damage than normal.
 * Unlocked by: Finish the advance campaign.

Olaf
Olaf is unaffected by snow, but moves through rain the way other COs move through snow.
 * CO Power: "Blizzard", causes a snow storm for one day, which lowers the enemies' movement range.
 * Unlocked by: Default

Grit
Grit's indirect fire units get 1 bonus range, his direct fire units have a 20% offensive deduction.
 * CO Power: "Snipe Attack", indirect units get 65% offensive bonus, and 2 range enhancements.
 * Unlocked by: Winning the mission "Max Strikes!" with Max.

Eagle
Eagle's air units require less fuel to move, and have 10% bonus to both offense and defense. His sea units receive a 10% deduction to both offense and defense.
 * CO Power: "Lightning Strike", all units gain an extra turn, except for infantry,but get -20% in offense and -30% in defense than in average.
 * Unlocked by: Win all Green Earth missions using Sami, then finish the campaign and bonus "Rivals!" mission.

Drake
Drake gets a 20% bonus of offense and defense to his sea units, and 20% deduction of offense and defense to his air units. It also rains more often when Drake is used in a match.
 * CO Power: "Tsunami", damages all enemy units by 1 HP, unless they were already at 1 HP.
 * Unlocked by: Win all Green Earth missions using Andy.

Kanbei
All of Kanbei's units have a 20% bonus to offense and defense, but cost 20% more.
 * CO Power: "Morale Boost", troops receive a 20% offense and defense bonus.
 * Unlocked by: Beat Campaign Mode.

Sonja
Sonja's units have a longer field of vision and their HP are invisible to the enemy. All of her units are "unlucky" and randomly deal 10% less damage.
 * CO Power: Increases vision for all units by an extra space and allows player to see into forests and reefs.
 * Unlocked by: Beat Kanbei's three missions in 8 days, 10 days then 12 days in that order, and then win the 3 hidden missions against Sonja.

Sturm
All of Sturm's units have a 20% defensive bonus, and a 20% offensive reduction. Terrain penalties do not apply to the movement of Sturm's units, except for when it snows.
 * CO Power: "Meteor Strike" Sends a meteor crashing into the area with the highest concentration of enemy troops, damaging by up to 4 HP.
 * Unlocked by: Unlocking every other CO except Nell.

However, when facing Sturm in Campaign mode, his units have a 20% offensive bonus, a 20% defensive reduction, and Meteor Strike damages up to 8 HP to each unit it hits. The terrain effects remain the same.