You can discard this card; add to your hand, 1 of your "Thunder Dragon" cards that is banished or in your GY, except "Thunder Dragonroar". If this card is banished, or sent from the field to the GY: You can Special Summon 1 "Thunder Dragon" monster from your Deck in Defense Position, but return it to the hand during the End Phase. You can only use 1 "Thunder Dragonroar" effect per turn, and only once that turn.
Thunder Dragonroar can be discarded to retrieve Thunder Dragon Spell/Traps.
Thunder Dragons’ playstyle revolves around discarding and banishing their monsters to trigger their effects. Their monsters almost fully consists of high-leveled monsters so Thunder Dragonhawk and Thunder Dragonroar are important for field presence.
A good setup card for a Thunder Dragon deck. Thunder Dragon Discharge will let you banish Thunder Dragon monsters from your deck to trigger their effects. You can then retrieve the banished monster by discarding Thunder Dragonroar.
Thunder Dragons Hundred Thunder is a generic support for Thunder monsters, allowing you to Special Summon all copies of a monster from your graveyard. Because the Special Summoned monsters are banished when they leave the field this can trigger the effects of Thunder Dragon monsters.
Aloof Lupine does not have anything to do with Thunder Dragons but his effect is very useful to them. Banishing and triggering the effects of 2 Thunder Dragons upon summoning, and adding a banished Thunder Dragon to your hand makes him a great setup card.
Thunder Dragon decks being composed of LIGHT and DARK monsters get access to these monsters who specialize in banishing. Banishing Thunder Dragons as their summoning cost will also trigger the Thunder Dragons’ effects.