Unfortunately you cannot test real wisp items ingame yet. This item worked a bit different, because it's basically just a change of his particle effects. For that method I entered the Dota 2 Test Mode by deleting all pak files in the dota folder, then overwriting Wisp's default particle effect with my changed one

Thanks for explantion.
And where can I find Io's particle effects? When I open his files in 3Ds Max, I find something like ball with texture (dmx.smd file of wisp) and something of pyramidal-form in, for example, his second skill smd file.
Not first time in modeling, but first time I ever try to understand, how effects working.
I want to change his tether ability or his own glowing, but can't find how can I do it. For example, if I want to change his own color, what file I must change and replace? Srly, I can't find a way, how can I do it, 'cos I don't try to do something like that before.

Sorry that I reply so late, I am in India right now with only a very limited internet connection. The particle files have to be extracted first via GCF Scape - I think there's a guide for particle effects on Cyborgmatt's Blog. After you extracted the pak01_dir file found in the /dota folder you can find IO's particles under C:\Program Files (x86)\Steam\steamapps\common\dota 2 beta\dota\particles\units\heroes\hero_wisp.pcf ; open those files with the Alien Swarm Particle Editor (that's a free game you can download in Steam); Voila, your particle files are ready for working.

Let me know if you need help, though it might take some time for me to reply. ;)

Hello, it's me again (new account)
My apologize for the long answer - no free time (work and studing in university) and frequently crashes of system. I think I'll try to do something this winter in January - and I'll try to connect with u if i can.
One question: you make this particles for old (i mean: very old) model of IO, right? I see here on your movie old color of hero. In summer patch changed effects structure (as I hear, in any case, death is displayed differently now and there is some changes in the particles of the basic model), i think, if u can rewrite item for new model it can be added (well, i hope, 'cos Valve's add some changes in system like... kinetic gem for example :D). Maybe it's need to raise the topic of this item on the forum dev.dota2.com? I don't know exactly, but there seems to have a section dedicated to dota 2 workshop.
Anyway, thx, I'll try to do something on free time after New Year )

@BlackSpiralDancer The model of Io doesn't really matter. If this was to be added as an item it would get a seperate particle file anyways, so Valve could basically change Io as much as they want without affecting this item ;)

Thx for the answer... okay, i'll try to work with it )