Align to another window

[Landiin]

OnTextChanged="Parent.Parent.AchievementCompleted.Top=/MainHUD.Effects.Top+89
Parent.Parent.AchievementCompleted.Left=/MainHUD.Effects.Left+90"

Unless something has change you can't address object the way you are trying to in the bolded code.

Once a window is created in display memory it becomes a child of _HUD. You do not need to worry about nodes like MainHud unless you are working with windows that are not in the display memory.

Basically the way the tree looks for windows that are in display memory is:

_HUD
|- Experience
|- Map

Hope this helps.