In addition to Tal's answer that points out that mashing in ultimate is the same as Smash 4, there is a trick that can help you get some more button inputs faster while using a GameCube or pro controller.

In the control settings you can rebind your d-pad from taunt to another input such as shield. This will allow you to circle the d-pad for four inputs in rapid succession.

_{Unfortunately, this means that you will be unable to taunt. So you will have to decide for yourself whether the fast mashing is worth the cost.}

In addition to Tal's answer that points out that mashing in ultimate is the same as Smash 4, there is a trick that can help you get some more button inputs faster while using a GameCube or pro controller.

In the control settings you can rebind your d-pad from taunt to another input such as shield. This will allow you to circle the d-pad for four inputs in rapid succession.

Below is ZeRo (competitive Smash player) explaining the d-pad mash trick:

_{Unfortunately, this means that you will be unable to taunt. So you will have to decide for yourself whether the fast mashing is worth the cost.}