Manta, the Behemoth of the Deep, was a creature that was shot with an arrow covered in three drops of a black liquid from a vial. The arrow was used in a crossbow to kill Manta, a creature ten times the size and strength of a dragon. It was believed that, like Deathwing, the Manta was unstoppable.
It was said that the black liquid was used to kill this beast 100 years ago which is about 90 years before Warcraft I.
If you want to learn more lore go to World of Warcraft Lore: Story and Geography of Ashenvale.
Where to start? Well, somebody would say all the way back to Warcraft I (aka Warcraft: Orcs & Humans or the First War), or maybe Warcraft II (aka Tides of Darkness or the Second War up to and including Wrath of the Lich King, Warcraft III is the best place to start. Also, this game then elicits more interesting questions. For instance, how Illidan Stormrage became so hated or where the Scourge started. You will learn all the history and geography of the Warcraft with our help and dedication.