League-of-legends – What stats of Malzahar’s do the Voidlings mimic

Life Steal and Spell Vamp don't proc based on the damage bonus source of the skill (AD versus AP), nor is it based on the damage type (physical versus magical). It's actually based on the kind of skill.

In general, Spell Vamp is the only drain effect that affects skills. All of Lee Sin's skills, despite all being AD-based physical attacks, use Spell Vamp and Spell Vamp alone. Akali is an example of a somewhat physical champion whose attack skills are all Spell Vamp-based (her innate Life Steal is to benefit her auto-attacks only). Even skills like Ashe's Volley, which applies her Frost Shot effect (but only that, the key point being as you'll read up soon), will use Spell Vamp.

Life Steal generally applies only to your auto-attack, but it also applies to skills that apply on-hit effects. For example, Blitzcrank's Power Fist deals 100% extra damage and pops the target in the air in addition to applying on-hit effects (for items like Black Cleaver). This benefits from Life Steal instead of Spell Vamp. Other examples of skills that benefit from Life Steal would be Irelia's Bladesurge, Ezreal's Mystic Shot, and Gangplank's Parrrley.

As far as I know, there is no skill which benefits from both Spell Vamp and Life Steal. It's always one or the other.

You mustn't mix up life steal and spell vamp.

Life steal steals on physical damage (meaning auto-attack for vlad). In fights, you very rarely use your auto-attacks to deal big damage because you're a caster.

Spell vamp steals on magical damage (meaning all of his spells), this is want you want if your plan is to steal more life.

• Zhonya's Hourglass is great because vlad's ult has low range but must be cast in battle engage to hit the most enemies and for the 15% extra magical damage. The two second invulnerability will allow you to stay alive in the heart of the battle if you get targeted.
• I also very often use Hextech Revolver with Vlad, but you need some AP. It's no use having 50% Spell vamp if you don't deal any damage.

Vlad spells cost life, the good thing about more spell vamp is you can get your life back faster with transfusions minion lines and you can cast life costing spells (specially Tides of Blood that stacks) with less impact on your life.

EDIT : I went to have a quick look at all the different Vlad builds. All (or nearly all) of the descent builds have hextech revolver in them with its evolution to will of the ancients - give more AP, more spell vamp and an aura :-)