Method to Acquire - Keep Douglas alive in Chapter 16 and he starts with you on Chapter 16x at two levels lower with the same stats. Unless you're playing Hard Mode of course, in which case he starts out with lower stats.
Damage - It's terrible. Unless you have the weapon advantage against a Myrmidon, he won't be dealing much damage.
Critical - It's horrible. Unlike the other three Armor Knights/Generals, he can't Triangle Attack. He's not worth a Killer Lance and a Killer Axe.
Speed - It's easily his worst stat. If only you could choose to swap his constitution with his speed, he wouldn't bad half as bad as he is. He'll be hit twice.
Dodge - He doesn't have a high dodge, but most enemies won't deal much damage to him. However, they will hit him twice and he will probably have a very low chance to hit them back.
Growth Rates
HP - 60%
Strength - 30%
Skill - 30%
Speed - 30%
Defense - 30%
Resistence - 20%
Luck - 5%
Average Level 20 General Douglas(no Hard Mode bonus)
HP - 53
Strength - 23
Skill - 17
Speed - 12
Defense - 24
Resistence - 6
Luck - 14
Total - 149
Supports
Elphin - 15/30/40 turns
Geese - 59/60/80 turns
Igrene - 59/60/80 turns
Percival - 15/30/40 turns
Cecilia - 15/30/40 turns
Lalum - 10/20/27 turns
Rating - 5/10. He's as good as Cecilia. If you're playing Normal, go ahead and use both of them and get their supports. They are both usable and won't be a burden. Just don't make the mistake of giving either of them Divine Weapons.