Mobile Optimisation Thoughts

Tile/Grid based TD will work better for mobile than "free" placement of towers, plus creep movement will be simpler when its restricted to 4 directions

Each tile can be: Path (unbuildable), Empty (buildable), Occupied (has a tower on it) or Decoration (unbuildable with some kind of decorative object on it)

Clicking an empty tile pauses the action and opens a "full size" window which has the tower buying options.
Pausing the game like this means the player can take their time with tower placement and not have to rush (which means they can focus on working with the smaller screen space), it'll make it a lot simpler/easier for mobile users.

I still think it'll need to be a Lite version of the PC version with smaller/redesigned levels to work with the smaller screen space. This however will be helped by the fact that each tower/pyramid will be 1x1 grid square as opposed to free placement (i.e smaller compared to the PC version).

For example an average level on PC might be 400x300 pixels of path/building space (with other space for UI, etc)
On Mobile it might be a 30x25 grid with the path going through it and all the UI overlaid/hidden until the player clicks