Changes from DotA

DotA, or Defense of the Ancients, was a custom map created for the Blizzard game, Warcraft 3 and Warcraft 3: The Frozen Throne. It borrowed many elements from the game and was based on its engine. Dota 2 is a complete game created by Valve on the Source Engine, however, and many differences exist due to copyright concerns and previous engine-related bugs.

Misc. Changes

 * You can resell items within the first ten seconds for full price.
 * Bottle can be filled with another rune even when full.
 * A Bottle with a rune in it is no longer a shareable item (in DotA it could not be used anyway).
 * AI practice bots
 * Manabars on allies
 * Crystal Maiden's Frostbite cannot freeze the enemy's fountain
 * Crystal Maiden's Frostbite works on Batrider using firefly
 * Fountain cannot be attacked
 * Hotkeys are customizable
 * Phase Boots do not prevent Skull Basher, Monkey King Bar, or items that grant Critical Strike from procing
 * Skills can be leveled up while dead.
 * Hero can no longer be deselected (except for selecting other controllable units, such as Couriers or pets)
 * Item shops are condensed (there are now only the main shop, side lane shops, and secret shops)
 * Orb Effects are called Unique Attack Modifiers.
 * Quelling Blade now works with Unique Attack Modifiers. (Also works on Kunkka's main target, not splash though)
 * Control Groups now save between summons for summoned minions (even when they die)
 * Cooldowns on abilities now show time left in seconds.
 * Items and many heroes have entirely new lore.
 * Mjollnir/Maelstrom currently stack with other Unique Attack Modifiers, overriding them on proc.
 * Orb of Venom is now a Unique Attack Modifier.
 * Eye of Skadi (both ranged and melee versions) will now work with items that grant Lifesteal, but are both Unique Attack Modifiers.
 * Phase Boots can use in conjunction with Batrider using firefly!
 * Most skills now stack. For example, skills that apply the common 30% MS 20% AS slow: Crystal Maiden, Lich, Jakiro; also Chen 's Penitence with Night Stalker 's Crippling Fear.
 * Extending the previous point, many skill and item interactions that existed due to its hard-coded nature don't exist any more. For example, Ghost Scepter doesn't remove Poison Nova.
 * Bonus damage from Shadow Blade is affected by built in crits from heroes such as Juggernaut
 * Bashes damage type and stun type doesn't depend on the range of the hero (used to be magical damage / physical stun on melee and the opposite for ranged). Instead, it depends on the source of the bash. Skills from heroes work like in DotA1, Monkey King Bar gives magical stun and damage, and Skull Basher works like melee.
 * Monkey King Bar gives uphill true strike against buildings, unlike DotA1 where true strike is a x1.0 crit and doesn't work on buildings.
 * Damage from multiple Monkey King Bars stack if they proc at the same time. It doesn't override any other on-hit effect either.
 * Fountain Hook with Chen does not work in Warcraft Dota.
 * Luna's Moon Glaive no longer has strange interactions with various orbs and critical strike effects and will not break on acquiring them or proccing them.
 * Rubick's Spellsteal now works on all abilities, whereas engine limitations prevented Rubick from stealing many skills in DotA. In Dota 2, there is no text above Spellsteal's projectile telling which spell was stolen.
 * Spirit Breaker's Charge of Darkness is not interrupted by items like Black King Bar or Shadow Blade.
 * Lion's Impale is now called Earth Spike.

Items
Due to copyright concerns, some items in Dota 2 have different names from their DotA equivalent.


 * Lothar's Edge is now Shadow Blade
 * Buriza-do kyanon is now Daedalus
 * Sobi Mask is now Sage's Mask
 * Ancient Janggo of Endurance is now Drum of Endurance
 * Kelen's Dagger is now Blink Dagger
 * Mask of Death is now Morbid Mask
 * Nathrezim Buckler is now Buckler
 * Khadgar's Pipe of Insight is now Pipe of Insight
 * Cranium Basher is now Skull Basher
 * Eaglehorn is now Eaglesong
 * Guinsoo's Scythe of Vyse is now Scythe of Vyse
 * Circlet of Nobility is now Circlet
 * Headdress of Rejuvenation is now Headdress
 * Stygian Desolator is now Desolator
 * Planeswalker's Cloak is now Cloak
 * Ogre Axe is now Ogre Club
 * Messerschmidt's Reaver is now Reaver
 * Boots of Elvenskin is now Band of Elvenskin

Heroes

 * Nerubian Assassin is now Nyx Assassin
 * Alleria the Windrunner is now Lyralei the Windrunner
 * Leoric the Skeleton King is now Ostarion the Skeleton King
 * Kael the Invoker is now just Invoker
 * Rexxar the Beastmaster is now Karroch the Beastmaster
 * Anub'seran the Nerubian Weaver is now Skitskurr the Weaver
 * Furion the Prophet is now Tequoia the Nature's Prophet
 * Dwarven Sniper is now Sniper
 * Clockwerk Goblin is now Clockwerk
 * Kel'thuzad the Lich is now Ethreain the Lich
 * Vol'jinn the Witch Doctor is now Zharvakko the Witch Doctor
 * Magina the Antimage is now just Antimage
 * Aurel Vlaicu the Gyrocopter is now Aurel the Gyrocopter
 * Aggron Stonebreaker the Ogre Magi is now Aggron Stonebreak the Ogre Magi
 * Nessaj the Chaos Knight is now just Chaos Knight
 * Obsidian Destroyer is now Outworld Destroyer
 * Pandaren Brewmaster is now Brewmaster

Buff Placers
Buff Placers refer to a group of Items in DotA that applied a buff to a Hero's attacks. Typically, they were also Orb Effects. Unlike Orb Effects, which do not stack for balance reasons, the Warcraft 3 engine was limited in that it only allowed one buff to be applied per attack. This meant that Buff Placers did not stack. In Dota 2, however, Buff Placers will now stack with each other. For example, Venomancer's Poison Sting will now stack with Desolator, even though both of them were Buff Placers in DotA.