Piratecat said:
I think I'd roleplay mine as someone who drew horrific powers and inspirations from the Far Realms. "They whisper in my ear. There are tentacles you can not see! They whisper to me, and I whisper back, and they placate me. Watch! If the squirming powers are with me, they will strike that creature with a... lightning bolt!"
Nice angle! Of course, I use the Far Realm heavily in my games, so this is right up my alley. Interesting factoid: except for the Spells requirement ("Able to cast at least one summoning spell of 3rd level or higher"), the Factotum can meet the requirements for Alienist quite easily by 8th level. I suspect many, if not most, DMs running games that aren't magic-light would let you get away with that requirement of the prestige class.
But as for hooks to RP a Factotum, how about technobabble? Star Trek series (any of them, pick your favorite) are infamous for this of course, but for this sort of roleplaying it works like a dream. "Programming computer to transmit Linguacode at their frequency and rate of speed." "We can hold their patterns in the pattern buffer and use the biofilter to scrub the organisms out!" "Somebody rigged this to keep the patterns in suspension so they'd just continually reinforce themselves and not degrade. But why?" "We discovered that flashing bright lights in a specific pattern would undo the effects of the addiction." ...Okay, sorry if some of those bring back bad memories, but you get the idea.
So you could say stuff like "Oh, the six-sided pattern of the tiles on the floor shows that this was laid by the Kobolds of Mesuth- pretty odd for a dwarven complex, I'd say, wouldn't you? Since they're legendary trapsmiths, I just put 2 and 2 together..." "Oh, I knew that by substituting the word 'Jexwlfab' in place of 'Sevorbeupstrey' in the sequence Rilsh used yesterday I could make the spell summon a celestial tiger instead of a fiendish one. And since we were fighting a demon, it made sense..." "...Oh, didn't you know that Positive energy powers the sun? That's why undead hate it. I used this solar collector to absorb some sunlight when we were outside yesterday, figuring it might come in handy down here- good thing I did, huh?"
If you go this route, you can even pick your favorite engineer (Scotty? O'Brien? Other?) to imitate in terms of quirks and mannerisms.