21 4-kana adverbs ending 'り'
From this video here (it's a multiple choice quiz with explanations, so go ahead and test yourself!) + a few I added!
1. にっこり sweetly (smiling), broadly (grinning)
2. ぼんやり absentmindedly, vacantly; dimly, vaguely
3. じっくり (slowly and) carefully, thoroughly, meticulously
4. ぐったり languidly, exhaustedly
5. くっきり clearly (standing out), distinctly, sharply
6. たっぷり plentifully, amply, abundantly
7. そっくり entirely, completely; exactly alike (e.g. in appearance)
8. こっそり stealthily, secretly, in secret
9. あっさり easily, readily, quickly, flatly (refuse)
10. きっちり exactly, precisely, punctually, on the dot
11. はっきり clearly, plainly, distinctly
12. ぐっすり soundly (sleeping), fast (asleep)
13. ゆっくり slowly, unhurriedly, without haste, leisurely
14. がっかり disappointed, dejected, downhearted, discouraged
15. ぴったり tightly, closely; exactly, precisely
16. ばったり with a clash, with a thud, with a bang
17. のんびり at leisure, in a relaxed manner, in a carefree manner
18. さっぱり feeling refreshed, feeling relieved; neat, tidy, clean
19. めっきり remarkably, noticeably, considerably, appreciably
20. ばっちり perfectly, right on the mark, spot on, bang on
21. ほんのり slightly, faintly