If you’re Crawling Chaos, you can awaken the Haunter for just 5 Power, and you don’t need a Great Old One, so obtaining it is a lot easier, BUT every other faction does get an Elder Sign when you do this.
The Haunter is explicitly a combat critter. It has a combat of 1 per enemy spellbook (so in theory 0-6, but in practice usually at the high end). I wanted to reflect the fact that one of the Haunter’s best-known characteristics is that it can’t survive well in the light. Therefore, it actually starts with a weakness, representing this disability – Fly The Light. This “ability” states that post-Battle, if the enemy scored only 1 Kill, it MUST be applied to the Haunter. If the enemy scored 2 or more kills though, you can target them normally.
The Haunter’s spellbook is really easy to get – just spend 1 Power as an action. Trivial. In fact, normally this is the first thing you’ll do after awakening the Haunter, which gives your enemies a one-turn window to try to take it out, before you get this frightful pre-Battle ability. It’s The Shining Trapezohedron. Before rolling combat dice, your enemy has to roll 1 die per unit he has in the battle. For each Kill he rolls, he must eliminate a unit (his choice).