From the Super Mario Wiki
Super Mario 64 / Super Mario 64 DS
In Super Mario 64, Klepto is seen in Shifting Sand Land. He holds a one of the castle's Power Stars, so Mario must reclaim it from his talons. Mario can attack the bird, knocking him out for short periods of time. Klepto will eventually regain his senses, and after losing the Power Star, he will attempt to steal who attempt to steal Mario's cap. Without his hat, Mario takes more damage when attacked. If he leaves and still has no hat, it will remain in the course he lost it in.
Klepto has the same Power Star and purpose in Super Mario 64 DS. He also appears in another level, the Sunshine Isles, accessible from the Rec Room. He makes a final appearance in Tiny-Huge Island, when the character is big. He is carrying, as usual, a star - except this time it's a Power Star. Additionally, though Klepto only steals heroes' caps, he will attack and cause harm if he glances Yoshi in the vicinity even if Yoshi uses any cap.
Mario Pinball Land 
Mario Party 3
In the background of Spiny Desert, three Klepto-looking condors can be seen on the upper left side of the board.
Mario Party 4
Klepto also appears in Mario Party 4 on Shy Guy's Jungle Jam. Players can pay him five coins to be transported to the other side of the board, collecting coins in the process. In Paths of Peril, Klepto will pick up players that falls off the stage.
Mario Party 5
In Mario Party 5, he has his own orb where, if landed on, Klepto will appear and take the character to another character's space determined by roulette, just like the Warp Space from Mario Party 4. In the instruction guide, Klepto's name is erroneously spelled Clepto.
Mario Party 6
In Mario Party 6, Klepto can be seen flying in the background of Pokey Punch-out. The Klepto Orb returns as an orb that can only be placed on a space. Any player who lands on it will be taken back to the start of the board. In the Solo Mode board Thirsty Gulch, another Klepto can be seen flying around the board.
Mario Party Advance
In Mario Party Advance, Klepto guards a treasure chest with a star. When the player arrives at Klepto's Ruins, his quest involves attempting to open the chest by entering the 4-digit code, giving them the hint that it is also his favorite word. When speaking, he has a tendency to stutter and repeat the word "for," indicating what the code is. By guessing the correct code (4444) and opening the chest, Klepto rewards the player with the Gaddget Map Maker. The ending states that Klepto changed the code to the treasure chest.
Mario Party 7
Mario Party 8
Names in other languages