First off, it says "Stride", not "Stance" for the name.

As for balance... hmm... at it is, I might invest a lot of money in my weapon especially the "viscious" property, then hide the first round of combat and spam it. Maybe make it so you can't resume it for 3 rounds after exiting it, or something. Also there are obvious abuse loop-holes for luck-blades and Nine-Lives Stealers to close. Also, WHERE they appear can be very important... if these duplicates appear next to you, or have to move out of you on their first turn, then that is a lot weaker than if you can drop a free flanker for the rogue, with 2 more waiting right behind that for if it gets destroyed.