Dodge staling is a mechanic in Super Smash Bros. Ultimate that penalizes players for overusing dodges. In general, the mechanic causes dodges to become slower and more vulnerable if spammed in a short amount of time.
The mechanic is named after stale-move negation, though it is otherwise unrelated.
When a player uses a sidestep, roll, or airdodge, their dodges become one level more stale, with a maximum staleness of 5 levels. Staled dodges grant less intangibility, while ground dodges animate slower (therefore taking longer to finish) and directional airdodges grant less distance. Intangibility maneuvers not mentioned (e.g. edge roll) do not affect, and are not affected by, this system.
The exact timings of intangibility and interruptiblity, as well as directional airdodge distance and speed, are character-specific and scale uniformly. For example, Mario's sidestep has intangibility starting on 3 for 15 frames when fresh, starting on 6 for 12 frames when fully staled, and various values in between for intermediate staleness levels.
Staleness diminishes at a rate of one level per 2 seconds, counting from the start of the last dodge used. However, an additional timer of 1 second counts from the interruptible point of the last dodge used, and dodges also unstale by one level when it expires. Therefore, dodges will always be fresh if used no more than once a second, whereas allowing them to stack up to full staleness will take about 8 seconds to fully refresh.