I hope the Windranger Arcana won't replace her Immortals

The windranger arcana is almost certainly a set, but as to what piece will be the important one that replaces stuff, I'd order them as follows (in order from most likely to least likely:

  1. Shoulder
  2. Quiver
  3. Head 4/5. Bow/Cape

As far as justification for this goes, as much as I don't think they want to remove compatiability with the sylvan vedette, it would be VERY colour scheme clashy. The yellow of the bird and the brown/gold of the jacket itself... I just don't see it working with the blues/greens of the arcana. Her body is also the main thing that changes - her clothing is entirely different, her legs are wrapped (or turned?) into wind, her arms are either minorly wrapped in wind or more likely painted, as is her face. I'd love for them to make it work but it seems unlikely to me.

The second most likely thing in my opinion is the quiver rather than the hair, simply because it appears to be absent from the art. Maybe her quiver is replaced by wind holding her arrows or something, your guess is as good as mine. This slot also doesn't have already have an immortal in it, making for a good candidate.

Next I'd put the head, but at this point I feel like it's reaching. This looks to me like it's probably just a nicer looking hairstyle that will come in the set. It's only higher than the other two because:

The bow and cape already have immortals, that colour scheme wise, match up with the arcana. The bow is very different, but the cape is not. I don't see these being the slots the effects are tied to, just based on the fact that the wind/paint changes would have to be tied to them, and they're both very disjointed from the actual model (One being held, and the other being a cape).

Obviously this is just my opinion though, so I could be entirely wrong. Hell, they might even retrofit a new style onto the sylvan vedette to make it work better with the arcana and apply it to the head? Anything could happen. For instance, Ogre's heathenous arcana takes the head slot iirc, and that modifies his body quite heavily and adds an entire mount.

/r/DotA2 Thread