jm2bok

That's exactly what I faced first when I began to learn Thai. It's not bad to attach to the normative pronunciation, as this way you'll be always understood. The problem (or I should said "challenge" instead) becomes when (surely our cases) we got early exposed to colloquial Thai language (as in the series) and all those kind of doubts arise. But that's the good thing, you'll be always motivated to learn something interesting and new :)

Hi! Well, I'll try to answer your question the most detailed I can, :P

1. In Thai words, there are a limited number of final sounds: vowels (Thai has nine basic vowel sounds), nasal sounds (n, m, ng) and stops (b, d, g). So, a pure Thai word will never end in any other sound different from the listed ones (Unless the word is a loanword/foreign one, in which case there possssssibly could be an exception and pronounce the original sound, but that's another story). In conclusion, each Thai word will have as final sound one of the listed above.

Then, what happended with the "s" in the transliteration (that would be the most adequate term instead translation) of the name "Mes"?

2. In written Thai, most of the consonant has two sounds: the main one, which takes when appearing at the beginning of a syllable, and the final one, which is... the name says it clearly hehe. For example, the consonant that represents the main sound "r" in Thai, will take the sound "n" when appears at the end of a syllable or word.
In the case of the consonant"s" (there are three diferent written consonants in Thai with this main sound), when appearing at the end of a word, they will take the sound "d".
Besides, when transliterating Thai words, the reference use to be the main sound of the consonant.
That's why the transliteration is "Mes", but they pronounce it "Med". This final "d" sound is not as strong as in English.

3. To the question about wheather Thai people find difficulties pronouncing certain consonant sounds. Effectively, Thai people tends to change (or even suppress) some consonant sounds. The "r" sound (as a main sound) is commonly changed by the "l" sound in the colloquial form of spoken language. That's why, for instance, the Thai word for "what" ("a-rai") is commonly pronounced as "a-lai".

Now... when there's a consonant group (or "cluster") with the "r" consonant (e.g. pr as in price, tr as in trace, kr as in krypton), Thai people (again, in the colloquial spoken form of language) tend not only to change to "l" sound, but to even suppress the "r" sound. And to make an example, I'll take an interesting case realated to the series: the name for the female character Plaifah, is actually "Praifah", because in the original Thai script for the name, the cluster is "Pr-", not "Pl-". And in the case of the name for the character "Prince" (which is a direct loanword from English), the raw transliteration would be "Preens", BUT.... remember what I said in the part 1? The final "s" will sound like an "d" sound.
Conclusion: "Prince" (transliterated "Preens" to resemble the most to the English pronunciation) turns to "Pind". The MIR character "Fuse" is exactly the same case, that's why it sounds like "Fewd".

I know all of this could sound difficult and twisted and tangled and even weird, but all of this has a reason (evolution of the Thai language through times).

I hope this notes to be useful to you and let me clear up your doubts :)

"Sawad-dii!" (And yes, the "d" sound in here is originally an "s" Thai consonant :P )

That's because the subber used a transliteration of the characters' names (he represented the exact equivalent of the thai consonants into the english alphabet). But... When a Thai consonant representing the /s/ sound appears in the end of a word, his sound change to /t/. And in the case Thun/Than, the difference relies on the way the vowel sound /u/ is pronounced in the name Thun: it sounds more like an /a/ sound, that is precisely the vowel used in the written thai name. So, in conclusion, the names Met/Thun are the better way to show english speakers the most accurate way to pronounce these names the Thai way. The pair Mes/Than are a transliteration from Thai writing system to English alphabet, and to deduce its correct pronunciation requires to have a little of basic knowledge of how Thai letters and sounds work.