DotA Orb effects

Items/Heroes with orb effects
Lifesteal
Mask of Death +10% Lifesteal
Mask of Madness +17% Lifesteal
Helm of Dominator +15% Lifesteal
Santanic +25% Lifesteal
Vladmir's Offering +16% Lifesteal Aura (melee Only)
SkeletonKing's Vampiric Aura +20% Lifesteal Aura at level 4 (melee Only)
Naix's Open Wound +25% Lifesteal for all who attack the targeted unit



Items with orb effect are the ones that you need to look out for. Lifesteal effect items overrides all the other orb effects. Only orb effects Aura stacks with the orb effects.

Orb effect plays a crucial role when you are attacking the enemies. As different orb effects will over ride

Orb effects don't stack and it's crucial that you know which orb effect over rides the other orb effects. Below is a table created by another person .
Here's the link: Orb Effects Table