Here are the cards you can use to boost the attack of Sea Dragon Lord Gashilnodon. Ancient Gear Cannon can tribute himself to inflict a small amount of damage to your opponent and lock out their Trap cards for the turn. Lost Blue Breaker can be tributed to destroy an opponent's backrow. You can crash monsters like Troop Dragon into your opponent's monsters to give Gashilnodon an attack boost. Troop Dragon would then special summon another copy of himself from the deck replenishing himself.