Hello, if you give the unit negitive mana regeneration, that unit will lose mana (See the Destroyer Undead unit in the normal game to see this done).
You can go into the preferences menu in the editor (If you have the frozen throne) and select "allow negitive values in editor". Then go to the unit's mana regeration field, hold down shift and click the down arrow untill the value become the negitive value you want. I belive mana regen = mp gained/sec. I.E. -2 will make the unit loose two mp per second, while a -0.3 will make the unit loose one mp every three seconds. (someone please correct me if i'm wrong)
Happy editing.
