The correct response to the situation described is:
Mario has shown that the two triangles are congruent. Three transformations are not always necessary when moving one triangle on top of the other.
This is true because congruence can be established through combinations of transformations, and overlapping triangles can occur with fewer than three transformations if the conditions are right. In this case, Mario's translations and rotations were sufficient to demonstrate the congruence of the triangles without needing a reflection.