Hearthpwn

It says "gain 2 mana crystals next turn". 

What it does - "give two temporary crystals which disappear when used.

Desert Nestmatron will not give you the mana back if cast from full crystals....Maybe that was obvious to some but it just lost me a game :(

The word "only" at the end of the card implies their temporary nature. As a rule of thumb, cards that refresh will only ever refresh up to your maximum amount. Trail Mix does not increase your maximum amount of mana crystals, but effective plays two coins the following turn,

Quote from xskarma >>

There's more quirks with Trailmix. Fairly sure I used the spell to get to 10 mana, but it did not reduce my Bouldering Buddy to cost 1.

It was just something I vaguely noted while concentrating on other stuff so not 100% sure this was the situation, but it would fit with the crystals not being "real" crystals for effects like this and Nestmatron.

I always assumed Bouldering Buddy has Manathirst that isn't called Manathirst. Only the maximum mana is relevant, temporary mana from coins and the like would not matter; just Hearthstone's law to never use keywords as keywords outside of their respective set again.

Omega cards like Omega Agent or Omega Assembly also worked the same. Perhaps a bit counter-intuitive, but this is hardly unprecedented.

Quote from lv426a11 >>

It says "gain 2 mana crystals next turn". 

What it does - "give two temporary crystals which disappear when used.

Desert Nestmatron will not give you the mana back if cast from full crystals....Maybe that was obvious to some but it just lost me a game :(

 Have you ever tried to coin out a Desert Nestmatron? Because I have lol. Spoiler: it doesn't refresh 4 crystals on turn 3. Temporary mana is treated differently in HS

You gotta type the whole card out my guy. As a former Magic player I must tell you "reading the card explains the card" haha, But sometimes thats some BS. You never truly know how a card works until you try it. The community often finds unique interactions. Some stuff just isn't super explained well. Such as "In three turns cast all spells you casted" does that mean three turns total or three of ours? Which is THIS TURN, your opponents turn, then your next one. Even though one would assume its "the next three turns" not HEY this one counts too. When a turn starts you already assume its already begun and shouldn't count. Such as counting today when you count how many days away something is. You just don't do that. You would start counting with tomorrow.

Thanks for all the replies - I wasn't really looking for a discussion, it was more a "heads-up" about how the card interacts with other cards, as I detest the number of interactions and effects in this game which are non-obvious.  I know some people will say "git gud" or words to that effect, but I really think Blizz should do better.  The sandwich making weapon is an excellent example...

Just to address some of the comments:

1) I know it's worded the same as the coin.  It just seems different.  Maybe it's because it's next turn rather than this turn.  I don't know.  Either way, the only reason I know how the coin works is because I've used it and it didn't do what I expected and based on the comment from D_Lord, i not the only one!

2) I didn't type the whole text but I don't think that changes the sentiment.  Writing out the whole text:

"Gain 2 Mana Crystals next turn only."

The word "only" to me implies that the mana crystals exist for next turn only i.e. the whole turn but not the next turn.  There's nothing to suggest they disappear entirely once used.  Normal mana crystals become empty - these should too and there's nothing to imply that they shouldn't.  Would it seem odd if (for example) trail mix took you to 10 mana, you used all 10 mana and end up with 10 empty crystals?  The two extra ones disappear at the end of the turn.  There are plenty of mana crystal based effects in hearthstone that (imo) should work with trail mix but for *reasons* don't seem to.

3) Regarding the manathirst comment (Dunscot) - I also think this is the wrong outcome based on the language.  Your example for Omega Agent should (imo) still trigger with trail mix (or coin).  The condition is "If you have 10 mana".   You have 10 mana - you can see the little mana crystals at the bottom of your screen and none of them are reperesented differently.  Logically you would assume that the condition is met and the effect should trigger.

Anyway, as I said, I wasn't looking for a back and forth about why it does what it does.  Just to let people know.