I also need help on figuring about the timing on frame trapping somone. I have seen players use two moves on someone where the first attack misses because the player is airdodges, but somehow seems to land the second move. Would I be able to pull off the aerials with Pit/Dark Pit is what I'm asking?
Frame trapping is relatively straightforward to use, but it's a fairly complicated process to find a legitimate frame trap.
To frame trap someone, you need to use a move, cause an air dodge, then be available to strike when that air dodge is over. The faster your response time, the more likely it's a legitimate frame trap. For instance, I found that forcing an air dodge with a back air from ZSS sets up for an inescapable flip kick response. Timing wise, that works, though it's not very practical from a positioning standpoint.
Interestingly, air dodging early prevents a lot of frame traps, since the dodging party can now respond before your second move hits. This means that even true frame traps have counters, and you must watch for it carefully. The one exception to this may be a forced air dodge into the ground. If you can make that happen, they pretty much have to eat your response.
Generally, to set this up, you want a move with low cool down followed by a move with fast start up.
I'm taking a really fast look at Pit, but don't take my word as law, there may be more to find. But, as a first glance, I don't see much that works. His down air has 27 frames of end lag on it, and Pit's air dodge (used as the example to save time) takes 32 frames. The invulnerability starts on frame 2, so subtract a frame and get 31 frames of waiting for a perfectly timed air dodge. You then need a move that starts in 4 frames as a response to that missed air dodge. If you are in the air, nair works. If you are forced to land, this doesn't work due to the added landing lag. NOTE. If your foe dodges early (say, they dodge your down air using the 10th frame of invulnerability) they will recover faster and the nair won't hit.
Alternatively, Pit's arrows are likely the other potential solution here. If your foe starts above you and you fire forward, wrap back around and force and air dodge, you can jump and up air, neutral air, back air, etc as a response.
Anyways, I hope that helps get you started on the search.