From the Super Mario Wiki
A 30-Coin from Super Mario Maker 2 (New Super Mario Bros. U style)
A large coin that has the number 30 written on it

First appearance

Super Mario Maker 2 (2019)

Effect on player

Awards the player 30 coins.

30-Coins are gold coins found in Super Mario Maker 2. As the name suggests, when collected, they grant the player thirty coins. They appear as a variant of the 10-Coin, in addition to the 50-Coin. Only five 30-Coins can be placed in a course; this limit is shared with the other 10-Coin variants.