When it attacks with at least two other creatures, which, in Goblin decks, should be always, creatures you control gain first strike AND trample until of turn
Making each of your attacking dragons deal 2 damage to any target, Defiant Thundermaw facilitates some truly devastating swings
When cast for its Overload cost, Cyclonic Rift acts as a one-sided boardwipe, clearing the field of almost everything but its casters permanents
Its a very common scenario in white: drawing cards at a high cost, or needing to compensate the opponent in some way
Its cost-reducing ability will make it much easier to cast some of your bigger creatures
In addition, the card can be called as a commander when played in Commander formats and has two additional abilities that can be triggered at various life costs