ok... so lets say you spam a bunch of these.
upgraded:
first turn: 6 total: 6
second turn: 12 total: 18
third turn: 12 total: 30
fourth turn: 12 total: 42
fifth turn: 12 total: 54
sixth turn: 12 total: 66
seventh turn: 12 total: 78
eighth turn: 12 total: 90
ninth turn: 12 total 102
total cost: 26
and you only need 2 air towers and an air mark to pull this off.
add some wryms and some more air towers and this deck would be epic.
NO. Any shuriken that are sent into the air will die immediately unless buffed, thanks to their 0 health - as has been already observed.
I'm assuming this is supposed to be a non-ranged weapon? You didn't say it's ranged, and shuriken are sometimes used as a melee stabbing weapon. If thrown, of course, you don't get it back, so conceptually the one that's in the weapon slot would be used in melee - otherwise it's behaving like a boomerang.
Interesting synergy with death effects, I like.
trio anyone?