Well, as I said most of these were decided late at night and just so I had some ideas for almost every one. To be honest, I really don't like a lot of them. So, that pretty much explains most of them, but there are a few I want to respond to specifically:
Acid: A weak irritant covering their skin that can cause burns with long exposure.
[color=rgb(255,0,0);]A bit too specific, if you ask me.[/color]
Really? I guess it could just be the irritant if you think so, but I like it.
[color=#ff0000;]I'm going to admit to an amount of personal bias here, I like my idea better.[/color]
Silver: Can amplify elemental beings they retain physical contact with
[color=rgb(255,0,0);]In the sense that Silver is highly conductive? A bit too farfetched[/color]
Pretty much. In the element guide in the reference topic it says that protosilver can amplify elemental energies.
[color=#ff0000;]Ah, I failed to notice that. In that case it makes sense[/color]
Mercury: Faster than other Matoran
[color=rgb(255,0,0);]What exactly is the reasoning behind this? Forgive me, I'm not very familiar with mercury[/color]
Well, I was thinking of the other name for Mercury, "Quicksilver."
[color=#ff0000;]The Element Mercury in the EM is a catch-all term for liquid metal if I'm not mistaken. I suppose on some level this suggestion could work, if only for the fact that no other element has it.[/color]
Ghost: Can create small, shortlived holograms, though Dr. O's idea sounds good too, maybe even better.
[color=rgb(255,0,0);]Keep in mind these are supposed to be minor physical traits, not extra powers[/color]
Yeah, I was unsure of this one too. Your idea would work just fine, although I'm a bit concerned about the fact that "Ghost" is referring more to energy structures than to ectoplasm.
[color=#ff0000;]Very true. But the point still stands. Fire is also a form of energy, but Ta-Matoran don't have energy-related skills.[/color]
Glass: Better eyesight if crystal doesn't get that, or possibly a slight weakening effect to solid substances?
[color=rgb(255,0,0);]Why not take a page from canon, if both Earth and Stone have enhanced strength, then why couldn't glass and crystal both have sharper eyesight.[/color]
Earth's ability is night vision. Po-Matoran are actually stronger. It just seems like Onu-Matoran are stronger because of all the feats they do. But if Onua was stronger than Pohatu, what would he need the Mask of Strength for?
I'm a bit hesitant to duplicate powers, as it makes the element seem less unique. Glass and Crystal are some fairly popular elements, and I don't want to generalize them both too much.
[color=#ff0000;]BS01 says differently. Onu-Matoran do get a degree of enhanced strength, though not quite as much as Po-Matoran do. This is the point I was trying to make. The relatioship between Glass/Crystal would be similar, with one of the two having a higher degree of enhanced vision than the other, while the weaker of the two would have an additional trait to compensate, much like how Onu-Matoran have Night Vision. As for what that trait might be: I suggest a resistance agains being blinded by bright flashes of light.[/color]
Salt: Always covered in thin film of salt.
[color=rgb(255,0,0);]Or they could eat more salt without growing thirsty or sick[/color]
Sounds pretty good, except how often would they need this? It doesn't have many possibilities for fanon. Then again, my idea isn't much better.
[color=#ff0000;]I was having just as much trouble as you with coming up with something plausible[/color]
Rubber: Can't channel electricity, flexible,
[color=rgb(255,0,0);]Probably more like resistance to electricity, they aren't [/color][color=rgb(255,0,0);]made[/color][color=rgb(255,0,0);] of rubber after all. Flexiblity sounds plausible[/color]
Well, Vo-Matoran are already electricity resistant, so that would be redundant. Invincibility to electricity sounds a bit over powered though now that I think about it.
[color=#ff0000;]So, flexibility then?[/color]
And don't worry, you don't sound snarky at all. A lot of your criticisms make perfect sense. I just hope someone else will have some better ideas.
Now that I look over the list in detail though, I'm really surprised Tar and Ghost got questioned so much while we have three new elements for magnetism. I can understand electromagnetism, but just merge that with electromagnets and get rid of magnets. They are all way too redundant. Why bother having to combine with a Fe-Toa when a Toa of Magnetism could probably do all those things on his own? Dry quicksand also seems a bit ridiculous, though now that I think back on it, it makes sense if you don't have a Toa of Water handy. Anti-gravity is another one. Maybe it can just be counted as one of those anti-elements we talked about a little while back. Most of it's abilities are already covered by gravity, so why bother combining, especially when shadow beings that will join with a Ba-Toa are probably in short supply?
[color=#ff0000;]I was wondering the same thing.[/color]