Damage types

In Dota 2, there are several different types of damage that can be cause by abilities and spells. Each type varies in how it affects enemy units. These types are magical, physical, mixed, pure, and direct HP removal.

Physical
Physical damage is caused by all regular attacks from all units. It is reduced by both Armor and Damage Block, is unaffected by Magic Resistance or Magic Immunity, and cannot effect Ethereal units. Examples of physical damage are Juggernaut's Omnislash and Slardar's Slithereen Crush.

There are several subtypes of physical damage, depepending on the source. Physical damage from heroes does normal damage against everything except Towers, which take only half damage from heroes. Piercing damage (such as that from Venomancer's Plague Wards) does reduced (50%) damage against heroes but enhanced (150%) damage to Lane creeps. This makes piercing damage much more effective at lane control than hero harassment. Siege damage (from siege lane creeps) does enhanced (150%) damage against towers but reduced (75%) against heroes.

Magical
Magical damage is caused primarily by spells, although not all do magic damage. Magic damage is reduced by Magic Resistance, does not affect magic immune units, and does 1.4 times damage against Ethereal units. Examples of magic damage are Leshrac's Split Earth and Beastmaster's Primal Roar.

Mixed
Mixed damage is a combination of magical and physical damage types. It is reduced by Armor, Magic Resistance, and Damage Block, but goes through Magic Immunity. It does not affect Ethereal units. Examples of Mixed damage are Beastmaster's Beastmaster and Leshrac's Diabolic Edict.

Pure
Pure damage is just that, pure. It ignores all Magic resistence. It does not affect units under Magic Immunity and does normal damage against Ethereal units. Examples of pure damage are Chen's Test of Faith and Tinker's Laser.

Chaos Damage
Chaos Damage is similar to pure damage but instead ignores all Armor values and Armor types. It does not affect Ethereal units. The only source of Chaos damage comes from Witch Doctor's Death Ward

HP Removal
HP Removal works by directly subtracting hitpoints from the affected unit. It ignores all damage reductions and affects units under Magic Immunity and Invulnerability and does normal damage against Ethereal units. Unlike all other damage types, HP Removal does not count as being attacked, so it will not interrupt Bottle or trigger any other on-attack effects. Examples of HP Removal are Necrolyte's Heartstopper Aura and Vengeful Spirit's Wave of Terror