Dig Deep

Pets cost diamonds and are fairly expensive. Diamonds are the slowest resource in the game. The last digger costs 20k diamonds so if you're going for 100% on this game, be a little stingy when buying pets. They do provide big upgrades for your digging but buying all 48 (12 islands times 4 per island) of them is prohibitively expensive. The cheapest way is to just buy all four from the first three islands.