Blitzplotter, thanks for the compliment on the GG_Curves_3D code. However, I agree that it's not the best solution for what you're doing here.
I don't agree that implementing a physics engine is the easiest, or even necessary to do a simple lob.
What I've done before with arcing arrows is to create a pivot, parent your grenade to the pivot (so the pivot is the grenade's parent). Rotate the pivot in the direction of the trajectory (away an upward from the character), then use MoveEntity in the z direction on the pivot. Also, gradually use TurnEntity to rotate the pitch downward as it flies. It will make a very smooth arch in the direction it's heading. By using a pivot to do the movement, you are free to rotate the grenade independently as it flies without affecting the trajectory.
I don't agree that implementing a physics engine is the easiest, or even necessary to do a simple lob.
What I've done before with arcing arrows is to create a pivot, parent your grenade to the pivot (so the pivot is the grenade's parent). Rotate the pivot in the direction of the trajectory (away an upward from the character), then use MoveEntity in the z direction on the pivot. Also, gradually use TurnEntity to rotate the pitch downward as it flies. It will make a very smooth arch in the direction it's heading. By using a pivot to do the movement, you are free to rotate the grenade independently as it flies without affecting the trajectory.