I picked the first option, since it's sorta right. This is kinda a long story, as in several paragraphs.... In short, I took my current online screen name from the rediscovered, original name (as in, the name I made up as the 'real name' of a character after playing under a different name for quite a while) of a character I roleplayed, in an online play-by-post forum (of sorts; there were hardly any rules, pretty much just 'no power trips and no planeswalkers,' and there was no game system or gamemaster; it was more like interactive communal storytelling than a formal PbP).
A little while after I got Internet access, around 8-11 years ago IIRC, I came across the Beyond Dominia site for Magic: The Gathering related news, discussion, deckbuilding, and stuff. One of a few such sites I found, but the only one that seemed particularly active and interesting to me. After lurking a few months, I stumbled upon the Beyond Dominia Roleplaying Mill, which I had not even noticed for some time while browsing the other Mills (forums), mostly the Rumor Mill (news/speculation/discussion forum). It was rather late in the BD RPM's life, as it had been much more active in the early 90's and such but slowed down in the mid-90's and eventually wound down to being closed in 2000, 2001, or maybe 2002 (I'm fairly sure it was closed down in 2000 or 2001).
By that time, I had been posting occasionally in the Rumor Mill as Mist Phantom, a screen name I threw together after thinking a while and considering the odd kinda screen names most of Beyond Dominia's users had taken up. Many used the names of M:TG cards or characters for their screen names. A few used the names of literary characters, such as Elrohir (the name of one of Elrond's sons, cousins, or nephews in The Lord Of The Rings; I'm pretty sure I remember Elrohir was Elrond's son?). A lot of folks though just used odd, abstract names, or random words, like Ped/Pedestrian, Shadow Darkmantle (IIRC), SageAdvisor, Defender, and so on and so forth (man, I wish I could remember more! *sigh*).
So I cobbled together the moniker of Mist Phantom for myself. I ended up using that also for my e-mail address. Not quite sure how/why I decided on Mist Phantom. I may have been marginally inspired by a Magic: The Gathering card like Mistfolk or some such thing (I think that was the name of a relatively-new card at the time, a kinda neat but weak card, common or uncommon). Before that, I had briefly gone by Master Dragon or Lord Phantasm online, the names of comic-book-style characters I had thought up and sketched as a kid. I latched onto Mist Phantom after that as a good, decent, simple moniker that wasn't too silly or wierd, and not likely to be already-in-use by anyone (or hardly anyone, at least).
When I decided to join in on the Beyond Dominia Roleplaying Mill, I came up with a character suited to the moniker of Mist Phantom. A partially-incorporeal apprentice mage and artificer, made somewhat phantasmal and constantly emitting mist due to a botched attempt by his mentor at resurrecting him with white, black, and blue magic, after the young man had dove in front of his master to take the brunt of a Fireball cast by one of his master's rivals. His master was able to wear down and chase off the rival after that, what with the smoke obscuring him after the explosion, and what with blue magic being the power of illusion and concealment and subterfuge. His mentor was only a dabbler in non-blue magics, but an archmage of blue magic, so tried his best to cobble together a resurrection spell with what he had available, before his apprentice's soul could reach the great beyond and escape his grasp.
With the apprentice's body reduced to ash, there wasn't much to work with, so the apprentice's soul could only partially recoup its material form, especially since Mist Phantom's master hardly had any experience or contact with white and green mana (the latter of which was antithetical to his blue mana specialty anyway), which dealt more with substance and life than his illusory/magic/spirit-focused blue mana. Mist Phantom ended up, shortly later, being stolen away from his homeplane and sent hurtling into the artificial quasi-plane of Phaema, by some (at the time) unknown entity. It was later discovered that the force which sent him to Phaema was the same one responsible for Mist Phantom's quasi-corporealty and constant emission of enshrouding mists; MP's mentor had inadvertently established a momentary contact with that entity's personal domain carved out amongst the aether between worlds, and it was that entity which allowed him to tap into the domain's mana for the cobbled-together resurrection spell.
Mist Phantom's mentor was one of the premier archmages of their homeplane, the best expert on blue mana in that plane, and working on developing a technique for blue-mana-shaping, forming spontaneous blue-mana effects without the need for formal, elaborate casting of specific, formulaic spells. Not anywhere near perfected yet, but his mentor was working on it, anyway, and it was that research that allowed him to attempt cobbling together an impromptu Resurrection spell using only a little white mana, a little black mana, and lots of blue mana (which unlike the other two, was mostly inappropriate to life/soul-related magic, but very appropriate to magic/mana-manipulating-and-altering spells).
Anyway, finally, Mist Phantom adventured for some years in the strange plane of Phaema, seeking after more knowledge of blue magic (the only kind he had learned from his mentor up to that point), and artifice to a lesser extent (which his second mentor, a friend of his first, taught him when he wasn't busy studying blue magic with his first mentor). He sought after a spell that could return him home or return him to having a physical, human body once more, rather than the vague, ghostly, mist-shrouded, half-corporeal form he possessed at the time. He met a lot of different people and helped out a bit at times, occasionally finding tomes of arcane lore to study and assist him in advancing his blue magic. Eventually he managed to become a decent artificer (crafting a flock of clockwork drakes to help build his Tower of Solitude, however briefly he was able to use it as a workshop, library, and home away from home) and slightly better than decent blue mage (hardly an average blue mage, but having traveled a whole lot and formed bonds with a large number of lands rich in blue mana, allowing him to harness a lot of mana despite only knowing a modest number of weak and mediocre blue spells). By that point he had become fully incorporeal due to some incidents, and had long since found that he was extremely vulnerable to the attacks of spirits, other incorporeal foes, and magical attacks. He had to use telekinetic spells (a common enough form of blue magic) to have any kind of interaction with corporeal matter. But, he finally discovered what he had long been searching for; an ancient tome in a buried ruin, containing an advanced blue spell to return physical form to incorporeal entities who had previously possessed a body of their own. Though needing telekinetic spells just to open the tome and flip through its pages, Mist Phantom had grown used to maintaining such spells by that point, and underwent the long ritual to gather the necessary blue mana and invoke the spell, restoring his original human body and clothing.
At that point he abandoned his descriptive moniker and took up his original name once more, now that he had regained his original body and had some hope of seeing his family and friends again, though he was still a long ways from finding any way to travel across planes, let alone finding his homeplane amongst the infinite expanse of the aether. His first name, if I recall correctly, was Arkhandus. I've since forgotten what the middle and last names of Mist Phantom were, but they all started with A (no, my own name does not start with A, I just decided to make MP's 'original' name an alliteration). Shortly after that, when I started playing some online games, I decided that Arkhandus seemed a suitable name for use in them. When I started playing StarCraft, I figured Arkhandus was suitably decent for a Protoss Executor's name, and Protoss was my favorite StarCraft faction, so I used that when I went on Battlenet. When I ended up registering on EN World a few years ago, I also decided to use Arkhandus, rather than my earlier tendency to use Mist Phantom as a forum moniker.
(There are no permutations of my real name that are ever free on servers, so I needed something that nobody would ever use...) The 'the second' part is because I lost the password to my original EN World boards name, which was blargney.
