Prepare to have your mind blown:
Words such as really and incredibly are adverbs. 🤯
So what are they doing in the adjective group? 🤔
The answer is, well, because they are adverbs and adverbs are the least rule-following of all the word types.
While it's true that in principle we use adverbs to describe actions and processes (they are called adverbs, after all), in practice we use them to describe verbs, adjectives, other adverbs, or even whole clauses or sentences!
As we've said in the verb groups lesson: adverbs are the chaos agents of grammar. They are shapeshifting goblins, whose function all depends on context.
(And we mean 'shapeshifting goblins' affectionately.)
Take another look at this snippet, and ask yourself, "What is the adverb doing?"