Spell lifesteal

Spell Lifesteal only comes into effect when using a spell that deals damage, healing for a certain percentage of the damage dealt by the spell.

Sources of Spell Lifesteal
Spell Lifesteal stacks fully with every other source of lifesteal and every other attack modifier, except with itself.

Working
The following abilities can lifesteal with Spell Lifesteal

1 The instantly killing effect of these spells also triggers Spell Lifesteal, healing based on the killed unit's remaining health.

2 Despite these spells using separate units to apply their effects, the damage sources of those are set on the caster, so Spell Lifesteal procs and heals.

3 The rum wear-off health loss does not proc Spell Lifesteal.

4 Only the splash from an Aghanim's Scepter upgraded Empower can proc Spell Lifesteal. The cleave cannot.

5 Does not lifesteal off of the area health cost. Only steals life when targeting an enemy to damage it.

Not working
The following abilities do not lifesteal with Spell Lifesteal

1 The cleave from Empower cannot proc Spell Lifesteal.