yugioh structure decks dark world Dealings - Deck: Dark World watch out! Yu-Gi-Oh! Dark World Structure Deck

The game plan for Crashing Footfalls is to cast either Shardless Agent or Violent Outburst and cascade into Crashing Footfalls

1 Scourge of Fleets

Also, you can activate it as a Free Chain targeting an opponent's monster, but be aware that it cannot interfere with your opponent's Synchro/Xyz Summon because it is your monster's level that changes

There is also the mild kicker that Seething Song loses instant speed when on Chandra, it cannot burst mana from 3 being on a four drop, nor on the turn it is played as it is still leaving you at -2 mana for the turn and really needs three activations before you are at +2 mana on initial investment