Rainbow Wave sends a rolling wave through your word — each letter bobs up and down slightly after its neighbour, with the colour spectrum spread across the letterforms.
rw-in brings the word up, then rw-wave runs a vertical offset per letter with a phase shift proportional to its index — that constant phase step is what makes the motion read as one travelling wave rather than letters bouncing independently.
The spectrum is core to this style. For the same wave motion in one colour, Slipstream gives you travelling letter motion without the rainbow.