From The Five Pillars

Halwen Spectres are created, using the Halwen Transformation spell, only for Swamp mages (or bought from the unit market). You need Halwen Wraiths for the spell to work. You cannot summon them like with normal units. The amount transformed per turn depends on your current Spell level (note: NOT the Spell Level you had when casting the HT spell).

Up till around an SL of 90, you only get 1 HS per turn.
From 90 to 130 you get 1 or 2 HS per turn.
From 130 to 195 you get 2 HS per turn.
From 195 to 270 you get 2 or 3 HS per turn.
From 270 to 340 you get 3 or 4 HS per turn.
From 340 to 350 you get 5 HS per turn.
From 350 to xxx you get 8 to 12 HS per turn.
Above zzz SL you get 15-20 HS per turn.

See the guide Halwen Spectre stack on how to use these flying critters as killers.

== Good against ==
Peasants

Weak against

Strengthen by