What if we had a VERY fast enemy (5, per se?) that, if on any given turn, didn't attack, it would use a default attack which lowered its speed by 1?
It would be a very "use it or lose it" sort of thing. Eventually, it would become a turret enemy like Energy Golems, which is why I suggest it be a War Engine (it rusts if you don't use it), and have a range of 2-4 in any of the 4 directions. Thus:
War Engine
HP: 50
PsP: N/A
Speed: 5 (to start with)
Attacks: Projectile (14 physical damage), Rust (Default: reduces own speed by 1)
Resistance to Heat (steam engine: heat only helps it burn hotter; it's a compromise between structural damage and better working. Instead of upping the damage done by 4 for every Heat attack sent its way [althrough that would be cool], it instead just gets a 50% damage reduction. Possibly used by the mechanics. Then again, they already have their golem tank units, so maybe this can be more of a Helenite thing.