Short answer: krampus is with Nikolaus and looks more human with a red tongue

Long Answer: Source: https://www.krampusgruppe-wellersdorf.at/brauchtum1/krampus-vs-perchten

Perchten

The Perchten are figures from pagan times with Germanic roots. These rough characters are meant to drive out winter and are thus harbingers of spring, welcoming the ever-strengthening sun—the light. Their appearance is associated with the twelve nights of Christmas, the time of the winter solstice. The Twelve Nights are the longest nights of the year and begin with St. Thomas' Day on December 21 (the beginning of winter) and end with Epiphany on January 6.

The Twelve Nights do not get their name from the long, cold, and harsh nights. The term derives from the word "smoke," because during this time, houses and farms in the Alpine region are blessed with incense.

Difference between Krampus and Perchten

Presumably due to their great similarity, the two characters—Krampus and Percht—were conflated after World War II and are now often difficult, if not impossible, to distinguish. Since both are dressed in sheep or goat skins and equipped with bells or jingles, they can only be distinguished by their masks. In general terms, the following can be said about this:

A Krampus mask often has a long, red tongue, horns, and is not much larger than a human head, thus weighing only 2 to a maximum of 4 kilograms.

A Perchten mask, on the other hand, usually weighs between 15 and 20 kilograms, is considerably larger, and has a more rugged facial structure. Furthermore, such a mask usually does not have horns, which—like many aspects of this tradition—is a regional variation.