Encode the backwards alphabet cipher

Question

Given a string of text that contains lowercase letters, encode it as follows: (I will be using abcdef)

• First, encode the alphabet cipher, but this time, 0-indexed. 000102030405
• Reverse it. 504030201000
• Loop through the string.
  • If the next two digits together are 25 or smaller, encode those two numbers. 5 04 03 02 01 00 0
  • Otherwise, encode one number. f e d c b a a
• Join. fedcbaa

Test cases

abcdef                          fedcbaa
abcdefghijklmnopqrstuvwxyz      fyxwvucjsrqponmlktihgfedcbaa
helloworld                      dbromylloha
ppcg                            gcfpb
codegolf                        fboqedema
programmingpuzzlesandcodegolf   fboqedemddkiobpzuzqdscmkhqerpb

Encoder (not golfed)

Remember, this is code-golf, so the code with the fewest bytes wins.

Answer 1

JavaScript, 126 125 bytes

s=>[...s.replace(/./g,c=>(parseInt(c,36)+90+'').slice(1))].reverse().join``.replace(/2[0-5]|[01]?./g,c=>(+c+10).toString(36))

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Answer 2

Perl, 73 + 2 = 75 bytes

Run with the -lp flag

s/./sprintf"%02d",-97+ord$&/eg;$_=reverse;s/2[0-5]|[01]?[0-9]/chr$&+97/eg

Answer 3

Haskell, 107 bytes

g.reverse.(>>=tail.show.(+3).fromEnum)
g(a:b:c)|r<-read[a,b],r<26=['a'..]!!r:g c
g(a:b)=[a..]!!49:g b
g e=e

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Answer 4

05AB1E, 31 26 bytes

-5 bytes after taking a look at Lynn's Haskell answer.

Ç3+€¦JR[Ð2£₂‹>DŠ£Aè?.$DõQ#

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Ç                     # codepoints of the input
 3+                   # add 3 to each (a->100, b->101, ...)
   €¦                 # remove the leading "1" from each number/string 
     J                # join into a single string
      R               # and reverse the string
                                                                          STACK
[                     # infinite loop
 Ð                    # push 2 copies of the current remaining string s   s, s, s
  2£                  # take the first two chars of s                     s[:2], s, s
    ₂‹                # are they (as a number) less than 26 (0 or 1)      s[:2]<26, s, s
      >D              # add 1 and duplicate the result                    (s[:2]<26)+1, (s[:2]<26)+1, s, s
        Š             # rotate the top three items on the stack           (s[:2]<26)+1, s, (s[:2]<26)+1, s
         £            # take the first or two first characters from s     s[:(s[:2]<26)+1], (s[:2]<26)+1, s
          Aè          # index with those into the alphabet                
            ?         # and print the result without a trailing newline
             .$       # remove the characters from s                      s[(s[:2]<26)+1:]
               DõQ#   # if s is now empty, exit the loop