What is the "reflection" of the mountain in the water? Is it an inverted castle peak virtual image or an upright castle peak virtual image? Why?

You can't just look at shadows from our perspective. Although we look into the water on the shore, the shadow we see is upside down, but it is actually a virtual image of a green hill standing upright. If you still don't understand, please look down.

Wood forms a reflection in the water, which is the reflection of light.

The mirror is the water surface, but the normal, incident angle and reflection angle are difficult to explain. Please see below.

1 tree can be regarded as countless points, so it can emit countless rays. If we want to study the normal, incident angle and reflection angle, we must analyze one of the specific rays. By reflection, we mean that these countless rays form a unified whole in the water (that is, in the mirror), which makes us look like a reflection directly.