- A reference guide and manual in Russian for Heroes 3.

???
Or, when you say "minimum number of movement points," do you mean not 1 movement point, but something else?

In this case, it's literally: "if a hero has enough movement points to move horizontally, then he can also move diagonally - provided there are no movement penalties." That is, either there are no penalties at all, or the hero has a corresponding level of the Pathfinding skill.

The other comments from Alex_R do not contradict my observations, so they have been added where appropriate. :)
Thank you for the information.