Coins (Silver and Gold) are the most common type of Money, dropped mainly by Guppies. If you are preparing for raining coin rampage, bring a money-collecting pet with you, like Stinky or Clyde, with a helper like Seymour or Nimbus. Meryl makes Guppies drop more coins.
Silver Coins are worth $15. A Medium Guppy will drop a Silver Coin every 6-7 seconds.
Gold Coins are worth $35. Large Guppies drop Gold Coins every 9 seconds. Vert also drops gold coins.