I think that two units would benefit (of course!) from a new ability, and that this ability would fit to them (overall).
This ability would be a unit spell akin to the Multi-hit spell of Moonguards and Ballistae, except that it would shoot a single missile rather than a salvo. As most of unit spells have now long cooldown times in TPC, this spell would be used once before going to melee. Units that are resistant to normal missiles would resist the damage as if dealt by a normal ranged unit. The question if the missile could target a flying unit (as with Multi-hit) is debatable, and perhaps the range could be lowered in this case? Also debatable is the impact of such researches as Weaponsmith (I'm not sure about Multi-hit and Fletcher either).
The Dwarven Infantry:
On the battle field, the only asset of this otherwise rather balanced but very slow axe-wielding unit lies on his resistance to any elements. They could also throw smaller axes from a short distance away. Given that the range of Minotaur axemen is 4, this spell shouldn't have a greater range, even if dwarven axes are allegedly lighter and more balanced. Perhaps, it could even go down to 3.
The idea is that upon closing their enemies, the Dwarven Infantry would hurl one throwing axe before joining in the fray. The range, as well as the sluggish speed of the unit, would prevent any hit and run tactic, anyways. Also, being a spell, the unit's effect in a tower would be unchanged.
The Barbarian Rider:
Fast, quite frail, and piercing damage-dealing units, the riders get in trouble fast even in numbers if they don't land critical hits. They could also throw a spear just as their infantry counter-part, without becoming a mounted tribesman though (even if their rendition on screen is just that, tribesmen on horses). Hence the spell.
Tribesmen's range is 4 (6 when upgraded). Therefore, range of spell could be 4 (or 3, given there is less momentum when riding), and wouldn't benefit from the Tribesmen's upgrade).
The idea is both to allow a riding party to throw a volley of spears before closing their enemies, and to allow for a hit and run tactic against slower enemies by harassing riders. In case the Barbarians get mounted archers (but if so, why not foot archers as well?), the latter tactic would become less wanted, of course. The long cooldown would not allow for repeated micro-ed hit-and-runs, only for just one, that would be deadly enough when performed in numbers.
To conclude, the suggestion above could perhaps be answered with but one same spell.
- copy most of Multi-hit define lines (up to the missile animation, why not?);
- one missile;
- range of 4 or 3;
- damage type is that of default unit damage type.
Or better, design two spells, one for each unit, that would allow for reusing Tribesman's or Axeman's missile animation, accordingly, as well as using the appropriate damage type. We would still lack the unit's animation.