-1 for bad spelling. An apostrophe is meant to show a missing letter or letters. Your hacked contraction doesn't need a apostrophe.
That is not actually entirely true, or is at least only partly true. An apostrophe is used to show a missing letter or letters, but it is also used to represent a glottal stop. This is seen most frequently in nouns, especially proper nouns. For example, while the common spelling is Hawaii, it more accurately represents to the proper pronunciation to render it as Hawai'i. Or consider names like O'Keefe, where it's being used to represent a phonetic variation on on the "O" sound that can't really be replicated with other letters. It might be even more appropriate to use an appropriately accented "O", but that's not easy to do on a keyboard. Then there's names like D'Urberville where the apostrophe sort of represents missing letters, except that De Urberville is awkward to pronounce because of the two consecutive vowel sounds, so you need a glottal stop to pronounce it properly, so when the name becomes a singular word over time, it becomes a bit of a gray area whether it represents a glottal stop or missing letters, or if maybe it's a distinction without a difference. Certainly such names often end up dropping the apostrophe (and indeed the glottal stop in prononciation in many cases). An example of this might be D'Arcy. There is of course, a famous character named Mr. Darcy in Jane Austen's Pride & Prejudice who is actually a very good example of this phenomenon and (at least speculatively) is a good example of some of the reasons it happens in the first place. So, of course, Mr. Darcy is wealthy British landed gentry - not actually with a noble title himself, but with a grandfather who was an Earl and his mother and aunt bore the title of Lady. The significance of the noble title is that D'Arcy is a french name and the aristocracy of England was mostly French for about 300 years or so up until the mid-thirteen hundreds (I would say it's complicated, but saying that it's merely complicated would oversimplify things). The point is that England had French-speaking aristocrats for a long period until being French went really out of fashion. So, the aristocracy shifted with the times and there was a tendency to democratize. This still went on over a long period of time and coincided with other social changes like the standardization of English spelling, etc. So names like D'Arcy in many cases switched to Darcy because reminding your English serfs/tenants/whatever that you were a French-descended noble ruling over them was not always a good idea. Of course, this was an incomplete process, with families named both D'Arcy and Darcy still around in Britain. Then of course there are names that add an extra complication like D'Eath - there are thousands of people with the last name Death in England (and statistically, you would expect maybe a dozen or so of them to be doctors and several times that to be nurses, which I am sure would be fun to hear over a hospital PA system).
Anyway, sorry, rambled on a bit there. The use of the apostrophe is just interesting. The point is though, that while replacing missing letters is one of its functions, it is rather a lot more complicated than that. Whatever else one might have to say about using "ma'sta" in the sentence the way the GP did, the use of the apostrophe clearly and properly indicates the prononciation that the GP was trying to evoke.