TL;DR
Counters energy denial by spawning retaliatory Jinxes that stun offending enemies, while Lanterns absorb incoming energy-block effects and explode into stacking team attack buffs.
Passive: When an allied hero suffers an Energy reduction effect from an enemy hero, a Jinx will be generated near the target. This effect can be triggered up to 1 time every 5 seconds for each allied hero. The Joyous Roamer will move to the Jinx and destroy it, launching a fireball at the enemy that inflicted the Energy reduction effect, dealing damage equal to 200% of the Joyous Roamer's Attack Rating and stunning the damaged target for 2 seconds. Every time a Jinx is generated, the Joyous Roamer gains extra Beast Energy.
Lv 3 The more Energy reduction an allied hero suffers, the stronger the Jinx generated. After the Joyous Roamer destroys a Jinx, the damage and stun duration of the fireballs will be increased, for a maximum boost of 75%. Team-Wide Attribute Buff: HP: 2.41%, ATK: 4%, DEF: 8.3%
Lv 6 Upon using the skill, the Joyous Roamer will summon 5 Lanterns in the air, which last for 10 seconds. Each Lantern grants immunity to 1 effect that prevents Energy recovery that enemy heroes try to apply on allied heroes. Lanterns will explode and disappear after the effect is triggered or when they expire.
Lv 9 At the start of battle, the Joyous Roamer will use Warden of Misfortune once, without spending any Beast Energy. Team-Wide Attribute Buff: HP: 2.77%, ATK: 4.59%, DEF: 9.53%
Lv 12 Whenever a Lantern explodes, it will increase the Attack Rating of all allied heroes by 10% for 8 seconds, for a maximum of 5 stacks.
Lv 15 For every 2 Jinx generated, the Joyous Roamer will provide a Lantern Shield to 2 allied heroes, with a shield value equal to 400% of the Joyous Roamer's Attack Rating but which cannot exceed 80% of the target's max health. The shield lasts for 9 seconds and grants immunity to 1 effect that prevent using Ultimates that enemy heroes try to apply on shielded heroes. Team-Wide Attribute Buff: HP: 2.89%, ATK: 4.8%, DEF: 9.96%
Lv 18 After destroying 3 Jinxes, the Joyous Roamer will transform, increasing its body size, and every time the passive effect is triggered, fireballs will be launched at an additional 2 target.