Your pieces simply step aside until your next turn and come back unharmed
In all cases, the card or effect will say something along the lines of You may cast this spell for [cost] rather than pay its mana cost, or You may cast this card from [zone] for [cost] instead of paying its mana cost. In other words: An alternative cost is something you can pay rather than paying the spells mana cost
There arent enough other die roll cards in the game to combine these with, and the ones that do exist arent all that fun
It pairs perfectly with other ocean-dwelling cards like Spawning Kraken or Quest for Ula's Temple, turning the bounce into a one-sided advantage while your massive creatures keep the cards flowing
Barring creatures like Progenitus, where its the whole point
The racers vary in their strength and abilities, but each will serve a purpose in your game