I HIGHLY recommend using the rules in this chapter, but they can make the game more complicated. If you wish to play a simpler game, you may wish to omit some of these rules.
In combat, a creature may spend 1 TS to move 1 unit. This is the simple, unabridged version of the movement rules. However, some creatures, or even characters, might have unique movement traits, like Flight or Burrowing.
Hexagonal Movement: It's simply a fact that a hexagonal grid is better at representing all of the possible arrangements that can occur on a 2D plane, so while this system is compatible with a square grid, I personally recommend using a hexagonal one. This means that diagonal movement is no longer a problem, since there are no diagonals on a hexagonal grid, except for...
Flight: Assuming the hex grid from before, you actually can move diagonally in one "step" when moving vertically, since you can move both up and in a direction and not skip an entire unit of space. This costs 2 TS per step, as does moving directly up. This means that upwards movement costs double what horizontal movement does. However, You can do the same when descending, and instead of costing double TS, the price per "step" is halved, meaning you move 2 units, possibly diagonally, per 1 TS spent. When put into practice, these rules are relatively simple, and they help keep combat near or on the ground, which is much easier to manage.
Climbing: A creature may climb up a surface if you, the GM, determine it is climbable. Outside of combat, you should settle this with a [V] or [Q] roll, but climbing in combat can be tricky. A creature may move both vertically and horizontally across the wall by spending 2 TS, they may not move diagonally like flyers can. A creature can jump off the wall for 1 TS, at which point they fall to the ground.
Falling: This one is less an optional rule and more one I hope you never have to use. Gravity hurts. When a creature falls a distance greater than 3 units, that creature takes (2^x)d4 damage, where x is the distance fallen minus 3.
The following rules add more variables to combat, which can be either a blessing or a curse depending on your player group.
Flanking: When a creature makes a defense roll against an attack, they make the roll at -1 for each enemy creature within 1 unit.