Quest: Kill Minions or Heroes within 1.5 seconds of hitting them with Chain Lightning. Reward: After killing 10 enemies, reduce the Mana cost of Chain Lightning from 45 to 25. Reward: After killing 20 enemies, gain a second charge of Chain Lightning.
Quest: Hitting at least 2 Heroes with a single use of Chain Lightning increases the damage of its bounces by 10, up to 400. Reward: After hitting multiple Heroes 20 times, Chain Lightning prioritizes bouncing to Heroes.
Quest: Basic Attacks against Heroes while Windfury's Movement Speed bonus is active increase Attack Damage by 1. Reward: After gaining 20 Attack Damage, increase the Movement Speed bonus of Windfury to 40%. Reward: After gaining 40 Attack Damage, Thrall permanently gains 15% increased Movement Speed.
Casting Chain Lightning on a Hero other than the last Hero it was cast on causes it to Slow targets by 8% for 2 seconds. Quest: Each consecutive cast against a new Hero increases this bonus by 8%, up to 40%. Bonuses are reset if Thrall dies or casts Chain Lightning on the same Hero twice. Reward: While at a 40% bonus, Chain Lightning's initial damage is increased by 25%.
Thrall was originally a support-type hero, possessing abilities that allow him to heal allies and debuff enemies. He previously possessed a bloodlust ability as well as lightning shield. His ability kit was transferred to Rehgar as the developers wanted Thrall to take a more offensive role.
Thrall was chosen to represent the shaman class by being the most well known shaman of Warcraft. In order to distinguish him from Za'Muro, he was given a cyber wolf to ride. This sparked the idea of mounts in the game.
A shaman version of Thrall was under consideration. This has since apparently been made a skin variant.
(Patch August 18, 2015) Note:Thrall’s Basic Attacks have received improvements in responsiveness, especially when stutter-stepping; Thrall’s first Basic Attack after Windfury ends will no longer have an abnormally long weapon period.