Method to Acquire - Visit the left house in the northeast or neither house on Chapter 9 and she'll pop up after around 10 turns. When she comes out of her house, so do a bunch of Fighters. To recruit her, speak to her with Lalum.
Damage - It's mindblowingly bad. If you give her an axe, her speed will go shooting down, which renders it worthless.
Critical - There is little chance that Echidna is able to have a Critical over 0.
Speed - She probably will hit twice on almost every unit in the Chapter you recruit her, and that's it. That is on Normal of course. On Hard, that Steel Axe murders her speed.
Dodge - It's her only not terrible stat and it's blown away by the fact that the enemies will still hit her with 41% chance, killing her before you recruit her.
Growth Rates
HP - 75%
Strength - 30%
Skill - 25%
Speed - 30%
Defense - 15%
Resistence - 15%
Luck - 20%
Average Level 20 Hero Echidna
HP - 42
Strength - 19
Skill - 24
Speed - 24
Defense - 11
Resistence - 10
Luck - 10
Total - 140
Supports
Geese - 59/60/80 turns
Lalum - 20/30/40 turns
Gonzales - 59/60/80 turns
Ward - 59/60/80 turns
Lott - 59/60/80 turns
Rating - 1/10. She's awful. In Hard Mode, don't send in Lalum by herself to recruit Echidna. In the rare event that Echidna survives the Fighters that start around her in Hard Mode, then send Lalum in to recruit her and get Echidna out of harm's way then arena abuse her. If Echidna dies, too bad, she isn't useful at all. It also doesn't help that all of her supports except with Lalum build slowly.