Find the letters that complete these five patterns

Complete the last line in each of the following five series:

Puzzle 1:

"Using" is E
"Desist" is I
"Visits" is E
"Design" is ???


Puzzle 2:

"Asia" is H
"Cuffs" is S
"Ender" is I
"Redness" is F
"Fuchsia" is ???


"Pro-tem" and "row" are H
"Ties" is K
"Cohesion" is A
"Casino" is E
"Hocks" is either a word, name, ??? or ???


Puzzle 4:

"Gross" is W or R
"Assign" is S
"Amassing" is E
"Design" is S
"Amassing" is S
"Arrows" is ??? or ???


Puzzle 5:

"Edna" is I
"Slang" is X
"Siege" is E
"Basin" is X
"Sin" is X
"Sin" is A
"Besiege" is X
"Signals" is ??? and ???


First person to solve all five gets the win.

Hint:

Each ??? stands for a single letter of the English alphabet.

Hint #2:

The puzzles are not related to one another, except that they are all based on the same principle. If you solve any one, you will rapidly solve all the others.

Hint #3, a quite cryptic one:

The very first parts of vague solutions can decode nothing: that's the core of these puzzles.

Hint #4, a more obvious one:

You want another hint?! Nag! Go botanist first, arse ulcer! O my! More clues? Rats! Rifts in a toboggan!

• I added a third, even longer puzzle, so I'm hopeful that it will be solved today. Dec 15 '14 at 15:52
• The puzzle idea is indeed great (and painstakingly constructed), but I still think your original posting was not. It only became good after adding the longer puzzles to it. I think this puzzle as a whole is much better. Don't call it "puzzle 1...5" have it the puzzle with part 1 to 5. This way, all alternative solutions drop out and your intended one becomes the only one. Dec 17 '14 at 14:22
• @BmyGuest Remove it? When am I going to have another chance to work "arse ulcer" into a puzzle? Dec 17 '14 at 17:46
• Just switched my downvote to an upvote. Feedback: Cool puzzle, but it just needed more data points from the get go. Dec 19 '14 at 6:22
• This puzzle is currently tied for 2nd best puzzle of 2014. :) meta.puzzling.stackexchange.com/questions/1759/… Apr 23 '15 at 6:28

Brilliant puzzle.

Puzzle 1:

U

Puzzle 2:

A

Puzzle 3:

T or P

Puzzle 4:

S or G

Puzzle 5:

I and E

Explanation:

They are palindromes, and every word is part of the palindrome too.

Individual solutions

The beginning, middle and end of the palindrome have been bolded:
using is e desist is i visits is e design is U
asia is h cuffs is s ender is i redness is f fuchsia is A
pro-tem and row are h ties is k cohesion is a casino is e hocks is either a word, name, T or P
gross is w or r assign is s amassing is e design is s amassing is s arrows is S or G
edna is i slang is x siege is e basin is x sin is x sin is a besiege is x si gnals is I and E

• Very close!!! But no unscrambling is required. You're almost there! Dec 17 '14 at 2:05
• Fixed, and I was right to upvote, and vote to reopen. Dec 17 '14 at 2:41
• Well done! Thanks for your support! Dec 17 '14 at 2:44
• And in case anyone didn't understand weird hint #3: The very first parts of "vague solutions can decode nothing" means the first letters of those words: V, S, C, D and N. That's the core of these puzzles, means that these are the central letters of the palindromes. I see you've already highlighted those, so you must have figured that out. Dec 17 '14 at 2:51
• Hint 4 itself is a palindrome, except for the bold part. Jul 25 '20 at 4:13

The letter is

I

because you

count the number of letters of the word that are also in your username, "Matt Malone"

which gives

"Using" is 1 (n) "Desist" is 2 (te) "Visits" is 1 (t) "Design" is 2 (ne) 

and then

take the letter that consists of that many dots in Morse code (e=., i=.., s=..., h=....).

• The idea of people reading my name over and over, carefully counting each letter, is great for my ego but it won't help you solve this puzzle. Dec 14 '14 at 4:17
• @MattMalone The problem is that this is 100% plausible, and there's nothing in the question to refute this theory. Dec 14 '14 at 7:24
• So wonderfully obscure and random while still perfectly plausible. I love this answer! @MattMalone I think xnor is just proofing by example that your question needs editing to be a valuable and not random puzzle. Can you add a (much) larger series? Or at her conditions which make the answer uniquely defined? Dec 14 '14 at 8:43
• @MattMalone " There is precisely one answer that fits." What's wrong with this answer besides it not matching your own method? Dec 14 '14 at 14:37
• This answer, while quite clever, is ad hoc. The puzzle is carefully and precisely written. There is one undeniably correct answer. Dec 14 '14 at 14:45

It's the letter

I

The pattern is that it's the second letter of the word immediately following it.

"Using" is E "Desist" is I "Visits" is E "Design" is ???

the next word is "Hint".

S

if you

wrap around back to "Using".

• Clever, using "Hint"! I like it! But I'm afraid that's not it. Dec 14 '14 at 4:49

I

Explanation;

The words having nothing to do with it, the pattern is E, I, E, I...

Alternatively...

Why?

You told us in the hint!

Or maybe...

I

Because...

Whichever letter comes first in the word, is the opposite (I is E, E Is I)
"Using" is E
"Desist" is I
"Visits" is E
"Design" is I

Perhaps it's...

I

A new idea why;

If the first i in the word is the 4th letter it's I else, it's E

Maybe it's...

I

Reasoning;

If the word contains an E the answer is I, else it's E

• Nice try! But no. Dec 14 '14 at 4:11
• I was just going to post that too, war spying. Dec 14 '14 at 8:45
• Sorry, you're still not there yet. When you see it, it will be strikingly, clearly the right answer. Dec 14 '14 at 13:41
• @warspyking I did, sorry. Auto spellcheck isn't always useful :-) Dec 14 '14 at 16:30
• @warspyking Not yet. But I bet someone gets it soon. Dec 16 '14 at 20:16