traditional real-time strategy games. Killing computer-controlled or neutral units earns the player experience points; the player gains a level when enough experience is accumulated. Leveling up improves the hero's toughness and the damage they inflict, and allows players to upgrade spells or skills. In addition to accumulating experience, players also manage a single resource of gold. The typical resource-gathering of Warcraft III is replaced by a combat-oriented money system; in addition to a small periodic income, heroes earn gold by killing or destroying hostile units, base structures, and enemy heroes. This creates an emphasis on "last-hitting" to land the killing blow and receive the experience and gold for doing so. Using gold, players buy items to strengthen their hero and gain abilities; certain items can be combined with recipes to create more powerful items. Buying items that suit one's hero is an important tactical element of the mod. DotA offers a variety of game modes, selected by the game host at the beginning of the match. The game modes dictate the difficulty of the scenario, as well as whether players can choose their hero or are assigned one randomly. Many game modes can be combined, allowing more flexible options. Development Blizzard Entertainment's 1998 real-time strategy game StarCraft shipped with a campaign editor that allowed players to create custom levels, complete with scripted triggers. One such custom map was "Aeon of Strife". Instead of controlling multiple units and managing buildings, players controlled a single hero unit as they fought against waves of enemies. Blizzard followed StarCraft with the real-time strategy game Warcraft III in 2002. As with Warcraft II and StarCraft, Blizzard included a free World Editor in the game that allows players to create custom scenarios or maps for the game, which can be played online with other players through Battle.net. Warcraft III also featured powerful hero units that leveled up and could equip items to boost their abilities, and the World Editor enabled mapmakers to create their own. Taking inspiration from Aeon of Strife and using the expanded capabilities of the World Editor, modder Kyle "Eulogizing" Sommer created the first version of Defense of the Ancients in 2003. The heroes could now sport different abilities and level up skills and equipment. After the release of Warcraft IIIs expansion The Frozen Throne, which added new features to the World Editor, Eul did not update the scenario and made his map