I have played this card in two campaigns now. Power Word reaches power levels that I haven't seen since pre-Key of Ys being tabooed. And if you were to ask me which I think is more powerful: a pre-taboo Key of Ys or Power Word, its really no contest. Power Word wins this contest hands down. I'm of the opinion that there are few cards in the game more powerful than Power Word.
What makes it so powerful? This is the setup I used when using it to fight: Tonguetwister / Thrice Spoken / Betray / Mercy / Confess / Distract. What has this let me do? Well, trivialize every scenario. I find a decent enemy, I Power Word it. Usually my first command that I give to all my minions is "Cower". Why? The enemy exhausts. It is not evaded so it remains engaged with you but will not attack you during the enemy phase. This means it will follow you around wherever you move. My second command is usually to Betray any non-PW'ed enemy at my location or Confess to get a clue. As the fighter in a 2p campaign, if I'm able to nab a couple of enemies early, I can frequently get half the clues needed to finish the scenario. And that's with me spending a lot of my actions fighting instead of focusing on clues.
I also took Wither. Yep, good 'ole Wither. If your minions have a fight of 3 but you need an enemy to die that has a fight of 4? Use Wither and lower its fight value so that your minions can finish it off. Or you can just Distract it if necessary. Whatever.
Any chance of you getting defeated? Nope. I sometimes find myself moving a space before fighting. Rather than using an action to exhaust them, then moving, then only getting one round of attacks, I would move (taking opportunity attacks from all 3 minions), then attack/heal, then attack/exhaust. I heal up almost all the damage they've done in the opportunity attacks. My partner and I are never close to death because I can use the minions to heal us up. Yes, healing is bad, but when it's actionless because I'm already exhausting them to pick up 3 testless clues in one action? It becomes very, very good.
Oh, and I'm sure that someone is going to say, "You can't give the same command twice!" But you can. Limit once per round per command. "Limit X per " is a limit that appears on cards that remain in play through the resolution of an ability's effect. Each instance of an ability with such a limit may be initiated X times during the designated period. Another copy of power word would have another instance of the same ability. So if you have 2 minions, you can activate the fight on both of them with Thrice Spoken and get both of them to deal a damage to an enemy at your location... twice. With 3 minions, you can spend all 3 actions telling each of them to fight, which causes the other 2 to fight. For a total of 9 testless damage.
Yes, there are some drawbacks. Health needs to be high for clues. Fight for fighting. Foot for evading. But I tell you, it is hilarious to have a Swarm of Rats as a minion (evade 3!) and while ordering the Rats to evade a scary elite, they are also crawling over you (or another investigator!) and healing you (or the other investigator!) for 1 damage. And the Rats are one of the worst minions you could cast this on.
I was playing Father Mateo with this combo (signature weakness: Serpents of Yig) and drew Mob Enforcer. It feels so good to have weaknesses that actively make your deck better. What other card in the game actively makes your weaknesses into strengths?
If you haven't played Power Word, I encourage you to try it. It's a card that you build around, but it's a spell, so cards to build around it are already cards you would play anyway. This card is so, so good.