Atlantis is an underwater sea race

:rolleyes:

2 skills having one effect. Or does one unlock the other?

Confidence only removes negative effects and only from the creature it is applied to - i.e., it doesn't give any bonuses, but makes everything standard as in the characteristics. :)
Tidal Wave removes negative effects and gives bonuses for several turns, but after the time expires, the bonuses disappear, and the negative effects return. :)
They are unlocked like Banshee's Cry, Archers' Rise for Necromancers. Like Magic Mirror for Mages. In short, like ordinary racial secondary skills. :rolleyes: