I tried making something like that a long long time ago, but it ultimately failed because the API does not tell you much about the shadow image.
There are a couple problems that need to be solved:
- The spawn position of the shadow image which is not always the same depending on the terrain. This is the biggest problem and prevents us from making it work accurately
- The different scaling of different maps makes measuring the distance hard. This can now be easily solved with LibGPS which didn't exist back when I tried making the addon.
- You need to track when the skill is cast, when the time runs out and it disappears and when the user tries to teleport outside the range (as it will change the skill back to summoning). For this you need to find all the abilityIDs and find the skill on the action bar, etc.
Besides that it is possible that you don't end up at your own shadow image if another NB is nearby, cast one for himself and you are closer to that one. Don't know if that's a bug or the intended behavior.
Overall it is pretty much impossible to tell the user anything accurately regarding that skill. If anyone is interested in making that addon, feel free to contact me and I'll send you my code.