Of the three Chaos cards introduced in this warpack the Staff is potentially the best imo. At least for our Tzeentch warlord; it seems crazy in Zarathur (admittedly many cards that are cheap and deal damage usually are) you can recur it with the signature support and notice that you can target the enemy warlord with the staff as well..

Staff of Change indeed. Changes living opponents into dead opponents. 

Interesting thoughts. But let me compare this to another card...

Dire Mutation: same cost for 1 more damage, but telegraphed (while mutation has Ambush), condition dependent (winning command) and only once per game round (as opposed to once per attack). OTOH, more favourable timing: command phase damage puts in the right side of Plaguebeast activations, and if you put it on a resilient unit, its more likely to keep giving you benefit throughout the game than Dire Mutation: Staff of Change has the potential to kill multiple targets, while Dire Mutation will only kill one.

All in all, I'd say this is a marginally better card than Dire Mutation. But here's the thing: my Zarathur swarm deck doesn't have room for Dire Mutation. Nor does it have room for this card.

Seems like a bully card to me.  Getting a couple in your warlord chain could offset the arriving exhausted issue.  You could use it to keep units from piling up on planets that you need to win.  Clear cappers off the board without needed to command snipe with the warlord.  I don't think it is a card for Zaraswarm.  This card is fixing a problem that the Zaraswam doesn't have right now.  I'd be more interested in what it does in big unit decks for warlords like Nazdreg, Ba'ar Zul, Kugath or maybe even Urien (who is often low on units and doesn't have token swarm to fall back on). 

Other than that I guess you could use it in some sort of hunt deck, but as Asklepios pointed out this is a telegraphed play.  I think it's more than marginally better than Dire Mutation considering you do two damage up front which in many cases can out right kill a command weenie or low end combat unit and we can do it potentially several times over the course of the game to different units.  Also there is far less restrictions on the target for this card.

I have yet to figure it out completely, but this card looks really good to me.

Being an attachment it gives Warpstorm protection and it quickly returns the investment..

I think Zarathur with a full direct damage approach can actually make a good use of this, being a conditional but repeatable Firestorm hitting for 3.

It's probably not a card you want to see in the early game, since you can't really be sure you'll be winning command, but in the mid game or as a finisher it works well.