In Super Mario 64, each of the 15 main courses has a Power Star that appears after you collect 100 coins in the level12. These 100 Coin Stars are unique because, unlike other stars, they appear directly above Mario when collected, and Mario remains in the level after collecting the star1. A textbox appears, and Mario can continue exploring the course1.
Here's how to collect 100 coins in some of the courses:
Collect the eight red coins and destroy the brown stones at the beginning of the stage3. Stomp Goombas and blow up Bob-ombs, and collect the row of yellow coins beneath the wooden bridge3. Run around the wooden stakes in the field to the left of the stone steps to release coins, and grab the ring of eight coins around the shrubs3. Use the Wing Cap to collect the rings of coins in the sky3.
This is one of the more annoying 100-coin stars because the coins are spread across a large level and swimming is slow4.
Another annoying 100-Coin Star because of the low number of overall coins and the constant swimming5. Start by grabbing the line of 5 coins on top of the rocky wall of the first room, then swim down and get the three coin rings and two coin pillars along the outside of the vortex in the middle5. In the second large room, swim to the bottom and grab the ring of coins near the clams5. Head up to the docks to find coins, use the purple switch to get to the floating platforms, and collect all 8 red coins5. Find and use the Blue Coin switch on the far floating platform to get 30 more coins5.