How the f does the shuriken work?

[Windrunner]

I read guides but I still don't understand. Everytime I throw it just nothing happens, no greys get destroyed at all. The cooldown starts anyway

[Mr. J.D. Gumby]

It destroys grey blocks that you have collected. Unlike Mono & Mono Pro, grey blocks you capture in Ninja Mono don't fade away - you have to shuriken them.

Use it to your advantage to make larger matches, to give yourself another 1.5 seconds to capture another block, and to guarantee yourself a Clean Finish.

[Windrunner]

oh thank you. I obviously misunderstood the ability then, thought it would destroy greys in front of me :)

[Mr. J.D. Gumby]

No worries - so did I. Probably most people did. It's not explained, after all.

[NovaTerran]

Should also note that shuriken is only on non-ironmode.
Grey blocks fade away on Ninja with Ironmode on.