How can i make system(or ability) like when i press a button the unit will move 50%faster, and lose 5 mana per second?
This means that the spell can be activated/deactivated at will, Venom....and lose 5 mana per second?
Note: you also need a trigger that checks when the unit's mana becomes 0, then remove the buff from that unit as well.
It doesn't automatically do that.
(Let me guess: you just need the triggers?)