Fire spell, level 4 – allows you to “burn” a fragment of darkness (terra incognita) within a radius depending on the hero’s mana points (similar to vision), covering a number of cells equal to basic/advanced/expert scouting range. This is not Dimension Door, but it is also an element of map control.
Dimension Door – as far as I can see, the only normal solution is to move it to water, since this fits into the concept (DD – Rampart guild – water; the tower remains with its native Fly and Mirror). Heroes who like to take water will practically not be cut off, although without slow in its current form, it would be much more difficult. And teleportation on the battlefield is somehow associated with the water element anyway. I suggest this not because I am a fan or anti-fan of Water Tower.
At least for Dimension Door, it might have been worth reducing the area by cutting off the corners – switching from a square to a circle; diagonal movement is already greater, and diagonals are also 41% "more expensive" in Might and Magic.
I agree with limiting the use of Town Portal to a specific number of times.
Baratorch made a great suggestion /topic/at/1113827/!
