Hidden around Grunty's lair is Cheato, Grunty's Spellbook. If you find him, he will give you secrets that will increase your eggs, red feathers, or gold feathers.
To find cheato the first time, go to Bubble Gloop Swamp to learn about the Wading Boots. Then, leave Bubble Gloop Swamp and go to the hollow log on the left to find some wading boots. After that, run to the back of the area to find a secret passage to an icy area with the Freezeezy Peak puzzle. Look for a rock to break. Once it is broken, go back into Bubble Gloop Swamp and transform into an aligator. Leave once again and go to the secret passage. Now you can fit through that small gap as an alligator. Cheato will be waiting inside to tell you the cheat, BLUEEGGS. Type in that cheat at the sandcastle at Treasure Trove Cove for 200 eggs.
Double Red Feathers
To find cheato the second time, go to the puzzle area of Gobi's Valley. Go into Mad Monster Mansion and transform into a pumpkin and leave. Go back to the puzzle area with Gobi's Valley and cross the narrow path to Brentilda. Once there, go into a small gap and you will find cheato once again. This time he will tell you the cheat, REDFEATHERS. Go back to Treasure Trove Cove and insert this code into the Sand Castle to get 100 red feathers.
Double Gold Feathers
Go to the Mad Monster Mansion level entrance area and to the left you will find a gate door you can break. Once broken, go into Mad Monster Mansion and turn into a pumpkin and leave. Now go back to the gate you just broke and follow the path until you find a small house. go in and use mumbo to transform into Banjo. Hit the switch to raise the water level in the water caverns. Turn back into a pumpkin to leave. Then go to the water caverns to find two other switches. Hit them for a timer to appear. Swim over to the Rusty Bucket Bay entrance area and swim to the top before the timer runs out. On the same wall as the pipe you just swam through is a staircase bathed in a green light. Cheato is waiting at the top of the stairs and will give you the cheat, GOLDFEATHERS. Insert it at the Sand Castle to get 20 gold feathers.