The starship captain passed his test. He's simultaneously angry and delighted. Of course it was too easy a test, with a half-human of some psionic power there to assist the humans in the crew, but he's still thrilled that something unexpected has happened. This human, this captain, is a worthy opponent, and he aches with the desire to... do what? Set up another test, maybe. Defeat the captain, watch him crawl. Or... lose. Privately, in the places he hides from the rest of the Continuum, he admits to himself that losing turned out to be surprisingly exciting, in a universe where he almost always wins.
But it has to be a challenge. He won't give the captain a cakewalk this time. He considers offering the man access to Q powers, but a bit of research on the human's history indicates that would be far, far too easy a challenge for the captain to defeat. Bad history with a human friend who developed godlike power. This human would know better.
The human has another weakness, though, one glaring out throughout his history. How delightful. Playing the game this way fills Q with a strange, thrilling sort of anticipation. In a universe of endless possibilities, anything could happen. As much as Q wants to beat the captain, see him grovel, make him admit to Q's superiority, the fact that it might not happen that way makes Q feel three billion years younger, excited about a project for the first time in aeons.
It'll require a change of form, of course. Q chooses a similar form-- still tall, dark-haired, still choosing a face stronger in character than in classical aesthetic beauty-- but the opposite sex from the last form, and teleports into the captain's bedroom moments before he arrives. Yellow's not her color so she doesn't wear one of his little Starfleet's uniforms this time. The captain knows his planet's history reasonably well, so she picks late 20th century ensemble, high heels, short skirt, light makeup, and sits on his bed with one foot on the floor, one foot propped on the bed, head leaning back against the wall.
The captain steps into his quarters and stops dead, staring at her. She smirks.
"Who are you? How did you get in my quarters?"
"Hi, Jimmy," she says, grinning at him. "It's Q. Like my new look?"