Will fit perfectly in Orc deck which lacks of AoE.

See this card working great with warpstorm as having an attachment exempts your nurgle unit from taking damage. Only concern is that it's likely going to end up on a nurgle with low HP thus creating a priority target that might not last long. May work best with the Death Guard Infantry.

So... let's talk Gun Drones.

Three things make Gun Drones a great 4/5 card:

1) Ambush Platform means that Gun Drones plays don't have to be telegraphed, and reduce the cost to 1.

2) There's a broad choice of ranged units to receive it, which means you can get AoE2 Ranged, which is dead strong.

3) Its a permanent benefit, which means you MIGHT get a chance to do it twice, though thats generally not terribly likely.

4) You can, in a pinch, play Gun Drones as a unit, though if you're doing so its 90% certain you're playing a Tau deck with not enough units.

On the downside of Gun Drones, you're investing two cards to gain an effect (unit and attachment) which opens up the opportunity for 2-for-1 answering, which can work against you.

Now that in mind let's look at this card.

Firstly, its fully telegraphed. There's no way to ambush this in, so you have to show it up front. Sure, it only costs 1 instead of 2, but with Gun Drones you'll normally be paying 1.

Second, none of the Nurgle units have Ranged, so you have to survive to strike with this. Fortunately, two of the Nurgle Units that can receive this have 4HP, but also both of those are awful cards, so to benefit from that resilience you have to run awful cards.

Third, its a one off benefit.

On the upside, it carries a shield, which Gun Drones doesn't, which balances out the play-as-unit versatility.

However, looking at context, while Gun Drones exists in a faction that has weak other access to AoE but strong access to attachment tricks and ranged, this attachment exists in a faction that has access to the best AoE unit in the game, and weak access to ranged. In fact, a Rokkit Launcha thrown in for a 3 card combo is the only way you're going to get Ranged AoE 2 out of this.

Right now, you'd be a fool to include this in your Ku'gath deck, even as a x1. Outside of a Ku'gath deck, you'd be triply a fool. Don't do it!

Good boost for Ku'gath decks and in general a better Dire Mutation option for that deck.

The only real downside being that it still needs to be attached to an Army unit (that can have Attachments) and should be Nurgle. 3/5 as a result.

This is nowhere close to Gun Drones but I feel that discussion is neither here or there as Chaos and Tau cannot ally and this work with totally different pools.

So far there is only 4 units availbe for this attachment and 2 of them are really bad and don't usually get in any decks. So Plaguebearers and Nurglings it's pretty much 2 tagrets you will be using this on - units with 2 health without ranged.

You cant play it as an ambush and it's one time use only... 

Pretty bad card  2/5. 

I may have been overly harsh - while my negative criticisms are unchanged, I think certain deck shapes can afford to run x2 of these. While its not the hardest card to answer and is quite a tough card to play, it does have a significant benefit when it plays successfully and goes unanswered.

So far there is only 4 units availbe for this attachment and 2 of them are really bad and don't usually get in any decks. So Plaguebearers and Nurglings it's pretty much 2 tagrets you will be using this on - units with 2 health without ranged.

You cant play it as an ambush and it's one time use only... 

 

There are only 2 units available for it in the right context, that is fully true. It also can be easy to remove certain Nurgle units that can hold it and it can't be played as an Ambush.

- However it also only costs 1 and thus gains you information.

- Under iniative (and without Ranged, because not even every faction has Ranged units to begin with) AoE 2 still hits rediculously hard. 

I can't say this card is bad. I can say that it would require better Nurgle units to make this card better. But this is in deck context and not in single card rating context.

I've been playing a Ku'gath deck with rotten plaguebearers, nurglings, and death guard infantry that has gained a lot of traction with 2x or 3x blight grenades. Not the MVP in the game but it typically shines once a game to win me the planet.