Create a discussion and I will gladly help. Sadly I'm not gonna be by a computer for the next week, but there are so many other Greenfoot programmers who will help you.

The reason the parabola disappears is because it's impossible to have two Y values for one X value when calculating with quadratic functions. I could fix this by not allowing the dots to have the same X value.

No problem for the help and good job. I don't know why this happens but the movement is very slow, this doesn't happen when I download the scenario, so my only guess is that it could be some kind of performance issue. One last thing is that there is a bug when you jump and land on a platform you sometimes jump through that platform and land in the middle of it.

Really good scenario, hope it's okay that I used the turtle code for one of my own scenarios. I have been working with this code for some time and I think I found one bug. In the turtles check method you have written: if (sqrList.get(i).isClosed() && sqrList.get(parent).getG() + cost < sqrList.get(i).getG()) // Check if new route to square is better Here the 'problem' is sqrList.get(i).isClosed(). If you take the turtle to (8,6) and then click on (9,3) you will see that the turtle moves in zigzag. If you remove the 'problem' the turtle will move straight up to (8,4) and then to the goal (9,3). I would love to know if this piece of code is there for a reason or if it's a mistake.

I got kind of lost on this project. I only made the engine for a rpg style game therefore the random world and the invisible walls. Maybe I will return to this project later, but the reason I stopped is because I find it hard to use Greenfoot for very large scrolling worlds due to performance problems.