Elfinkazes come into play at the start of the Onslaught Phase, on top of any active units or spires that have the talent Elfin. This includes units ready for deployment in the fortress gate, as long as they are not grouped underneath other units. You must choose whether the elfinkaze is coming out on its Glidebomb side or its Save side when it enters play.
Elfinkaze can stay on that unit or spire without being considered a group. Both the elfinkaze and the unit or spire underneath it are considered active and can attack and be attacked.
When the bottom unit moves, the elfinkaze goes along with it.
The elfinkaze can also move off of the unit. Its movement is allowed by its Roost Roam ability, which says that you may choose how much of its movement to use and where it moves. Its movement stat is dictated by the Roost number it was most recently, or is currently, perched on.
If an elfinkaze starts its turn not on a roost, perhaps because it moved away the previous turn or its perch was defeated, it has to either use its movement to return to a roost, or use its Glidebomb or Save talent.
Glidebomb and Save are both triggered either before or after the elfinkaze’s movement. Glidebomb will deal 2 damage to all adjacent units, fortress gates, and spires; it will also defeat the elfinkaze which is then returned to your barracks. Save allows an adjacent unit to recover up to 4 health. Again, the elfinkaze is defeated when this talent is used.
If elfinkazes are the only minions in play, the wave ends and the elfinkaze should be returned to your barracks.
Something often forgotten with elfinkazes is that they may attack, though they do not have to do so.