Coin duplication

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Coin duplication, often shortened to coin duping, is a glitch that can cause the rock blocks in the Cascade Kingdom that normally drop a ring of eight coins to drop duplicate coin rings, in order to harvest up to 48 coins. The glitch involves hitting the blocks at a precise angle while using the T-Rex capture, and can be performed in the Cascade Kingdom overworld as well as the Dinosaur Nest room. When used in the Dinosaur Nest, it is the fastest known way of accumulating coins excluding Luigi's Balloon World.

Coin duplication is only possible on versions 1.0.1 and later, since it utilizes extra hitboxes of the T-Rex that were first implemented in 1.0.1.

Explanation

In versions 1.0.1 and onward, the T-Rex has six independent hitboxes that can all collide with a rock block at around the same time. This will cause the block to register up to six hits rather than only one, and drop a corresponding number of coin rings (which can result in any multiple of eight coins up to 48).

This is performed by walking into the corner of the block such that the T-Rex's body is above it with its legs straddling the sides of the block. Generally, it is easier to perform by walking into the block slowly rather than at full speed.

Because the coin rings all spawn in the same location, it is generally not visually apparent that they have been duplicated until they are collected. However, the sound of the coin ring dropping can be heard playing multiple times at once, which gives an indication of success without needing to keep track of the coin counter.

Speedrun usage

In speedruns that require accumulating a large number of coins, such as 100%, coin duplication is the fastest available method since Luigi's Balloon World is generally disallowed in speedruns. It is performed in the Dinosaur Nest room, since the room contains numerous other coins from destroying Burrbos and rock blocks in addition to the block where coin duplication is possible, and it can be repeated for as many iterations as desired by exiting and re-entering the room.

The route involves heading directly to the T-Rex and capturing it, following the path around to the right where coin duplication is performed, and continuing to follow the path before making it back to the center of the room where the remaining Burrbos can be killed for coins. This method provides around 265 coins per minute, which is well over the approximately 195 coins per minute given by the second fastest coin grinding method, the Dashing Above the Clouds bonus level in Bowser's Kingdom.