Haste's description states that it gives +2 Init and a further +2 Init per Air Shard - however, what it actually seems to do is boost init AND immediately give the targeted unit a second turn.

This allows some pretty crazy abuse with casters - in my recent game, I used two casters in my army, the first would start a multi-turn spell like Fireball or Dirge of Ceresa, then my second caster would caste Haste first on herself - giving her another turn immediately, then on the first caster, giving him another turn immediately and triggering the Fireball/Dirge before the enemy army had a chance to spread out.

This isn't necessarily broken or anything, I'm just not clear on if this is the way the spell is supposed to work.