100 Coin Comet

Not to be confused with the standard 100 coin Star featured as the 7th Star in most courses, "100 Coin Comet" is a challenge present in some hacks that require the player to gather 100 red coins (or equivalent)to spawn a Power Star. These Stars are designed after the Purple Comets from the Super Mario Galaxy games, which provided the player with a challenge that required them to explore an entire level to find every single coin.

Similar to the original comets, the 100 coin comets are special challenges separate from the usual level's objectives; these Stars usually do not have any enemies or other coin types within the level, the red coins being in most cases the only collectables. The red coins are almost always laid out on or just above the level's ground geometry, and are easily reached by Mario without significant difficulty. Once all of the coins or a certain number of them are collected, the Star will spawn. Supposedly, the first SM64 ROM hack to feature this concept was Star Revenge 2: Night of Doom.

Since Super Mario 64 was not originally designed to have levels with more than 8 red coins to collect, the player will likely run into two minor glitches while collecting the coins:

Coins collected before the final 8 will show a zero as they are collected (this is only a graphical bug, the coins count up properly regardless)
Coins collected before the final 8 will also not play the proper sounds; all coins before the 48th remaining coins will not play any sound at all (except for the normal coin collection sound). For the final 48 coins, the 48th coin up to the 9th will play a random selection of sound effects when collected. The final 8 coins may play various other in-game sound effects, but may also have the correct sound effects play for their collection.

Most levels with this idea are simply clones of the Purple Comet concept, having 100 red coins, the Purple Coin music from Galaxy and no time limit, but there are some exceptions:

Super Mario Apocalypse: Green Salvation adds a Green Demon Challenge to its 100 coin comet, with a homing "Mario" (mushroom retextured) constantly chasing the real Mario around.
Lost Universe 1.5 has coin comets as its first two Bowser "battles", with 50 and 100 coins to collect respectively in order to grant Mario the Key.
One Must Imagine Mario As Happy has a coin comet-style Star to collect in its fourth course, but it does not require every single coin to be collected- only the vast majority. It also still has many enemies around, making it a much tougher challenge.

100 Coin Comet

List of Hacks Featuring a 100 Coin Comet Star:[]