What I would always do is:
-Add a plane, subdivide it a bit
-Raise or lower some faces until satisfied
Doing this has often led to having some faces not behave like it should, and would cause the player to sink slightly into the ground.
It also made faces change shapes when going in/out of edit mode…
Here’s an example.
-Notice how it SINKS into the ground, and
-when going in and out of Edit Mode, how the faces change.
This happens all the time, is there a better way to make terrain?!