I'm aware the API is still a work in progress, these are purely just suggestions
Callbacks
Create/Delete Object - This is just a much more efficient way than storing object by looping through them every frame
Add/Update/Remove Buff - Just useful, most champion script require buff logic
Send/Receive Packet - Useful for creating custom callbacks and other features (for anyone worried, it's perfectly safe as long as you don't send anything)
New Way point/Dash - Path analysis/tracking dashes
Process Spell - Please add projectile network ID to spellProc struct
Wnd Msg - Useful for menu/UI
Note for create object callback: Other software have hooked this quite deeply which requires you to delay the callback to get necessary properties. Please don't do this.
Functions
Cast(slot)
Cast(slot, x, y)
Cast(slot, unit)
Cast(slot, x1, y1, x2, y2)
Please make this an overloaded function, it just make the API easier and better looking
GetMousePos2D(void) - Get screen position of mouse
GetNavigationPath(unit) - Returns unit's current path/way points (I really, really want this <3)
IsWall(x, y, z) - Returns true if provided position is a wall
IsBrush(x, y, z) - Returns true if provided position is a brush
IsTargetable(unit) - Returns true if unit can be attacked (Vlad Pool/Zyra Passive/Zhonyas etc)
Bind(callback, function) - Binds function to callback
Unbind(callback, function) - Unbinds function from callback
Makes the whole callback system a lot neater, for example Bind("ProcessSpell", OnProcessSpell)
This is all I can think of for now, will probably add more when I get back from work