I see that many peoples still confused by changing Return mechanic. It's known too as "Dota 2 return mechanic".
And yes, it will never changed back.
Blade mail.
Return deals same damage type and same amount of damage. Looks like "Hero damaging himself when attacking in Blade mail".
There's 4 main damage types in game:
Physical — taking damage reduced by Armor (especially good boost from Guardian Angel and Cold Embrace) and fully blocked by Ghost form (ghost scepter, etherial blade, decrepify, etc.).
Magic — taking damage reduced by Magic Resistance and fully blocked by Spell Immunity (Bkb, Repel, Rage, Blade Fury). Increased in ghost form.
Pure — taking damage can't be reduced normally but Blocked by spell immunity.
Divine — taking damage can't be reduced or blocked normally.
There's exist taking damage amplifiers too, like: Bloodrage (bloodseeker), Penitence (chen 1), Soul Cather (shadow demon 2)
Damage that enemy takes based on His armor, His spell resistance and His modifiers.
Damage that takes attacker based on attacker's armor, resistance and modifiers.
And all lifesteal (physical and spell) based on damage that enemy takes really, after all reducing.
This way good comboes and countering:
1) Heavy armor and resistance VS Return, like DK, Shreder, Huskar passives, Anti-mage's spell shield, etc.
2) Reducing enemy armor/spellresistance or increasing damage they'r taking, like Amplify damage (Slardar 4), Penitence, Soul Cather, Flesh Golem form (plague aura), Natural Order (Tauren Chieftain aura), Assault cuirass, Veil of Discord, Venge's wave, Acid Spray etc.
3) Unique lifesteal from all instances — Naix's Open Wounds, which can heal as VS blademail, as By damaging cursed enemy by blademail or dispersion.
4) Lowcost mass heals like Vladimir and Mekansm.
5) Taking armor for phys damagers or spell resistance for casters. Ex. Activated Glimmer Cape on yourself for defend from returning magical damage. Ex. Casting Finger with 1025 dmg under Glimmer's Cape effect will give back only ~370 damage from enemy BM. If he will in ghost form, he will take more, but returning damage will not changed.
6) Silver Edge reduces all outgoing damage by 40% additionally to removing passives. That means Blade Mail damage will reduced too and dispersion totally disabled.
For example
Hero with 45-50 armor and 45% lifesteal (Vladimir + Vampiric aura + Assault Cuirass) will even heal vs enemy Blade mail when enemy have only 15 total armor.
If anyone have smth to add there, write it below, please.