Heat Wave is one of the Mystical abilities. You need 8 Mystical use points to be able to cast it. If you have 7 use points plus your bonus 1 pt for being a Mystical user, you can still cast HW even though it won't show up on your M menu. This is true for every M ability that costs multiple points.
Heat Wave is an offensive attack. It does 2.5x your normal attack damage.
|Damage = [(YourStrength/2) + rand(0, (YourStrength/2) - 1)] x2.5 - EnemyDefense. (Round down fractional damage)|
Strategic Use Edit
Heat Wave is a moderately powerful attack, and can be used on players or the dragon, or even a forest monster. It's usually used only when other skills have been depleted first, and this is what's left. Though T skills are 3x as powerful, there is a pervasive feeling that the HW doesn't quite deliver on its promise of 2.5.