The next (and last) letter is C. Just as a countdown counts backwards, this series is "countdown" spelled backwards.
D
W
D
The next letter is D. The pattern is every fourth letter. Ie. a b c D e f g H i j k L m n o P and so on...
Next three letters are: e n d
d
The series appears to be following a pattern where the letters are increasing in alphabetical order, skipping some letters. The pattern is A (skipping B) D (skipping E, F, G, H, I, J, K, L, M, N) O (skipping P) Q. Therefore, the next letter in the series should be R.
J. Those are the initials of the months, backwards from December through July. The next would be June.
S, S, O, N, D etcItalian:UnoDueTreQuattroCinqueSeiSetteOttoNoveDieciECC
The next letter in the sequence Z A V E R N follows a pattern where every second letter is skipped: Z (skip Y) A (skip B) V (skip U) E (skip D) R (skip Q) N. Continuing this pattern, the next letter after N, skipping M, would be O. Therefore, the next letter in the sequence is O.
It looks as if every third letter is an "r"; the remaining letters are in sequence.
The next group of letters in the series is "on." The pattern involves skipping one letter between each pair: b (skip c) d, e (skip f) g, h (skip i) j, k (skip l) m. Following this pattern, after "k" and "m," the next letters are "o" (skip n) and "n."