N4 — outside your level filter
Modifies a predicate directly and takes no copula, so there is no paradigm to conjugate.
すっかり
sukkaricompletely; entirelyN4adverb
Readings and definitions from JMdict, © the Electronic Dictionary Research and Development Group (EDRDG), used under CC BY-SA 4.0; levels from the Tanos JLPT lists.