Auto Cast Spell Buffs Help ME!!

[Swerd]

Sorry for the poor title but im trying to make a spell similar to cold arrows but i want one more thing added to it.My ability is the user throws a axe really quickly so it pierces the skin causeing the enemy unit to take damage over time for 2 seconds or so and move speed and attack rate reduction i cant find any auto cast spells that have the damage over time function can somone help me and tell me what to do?