Arcfire is a bit tricky to use against good players imo, cause they can punish it really easely. Try to use it a different way each time : Sometimes short hop, sometimes don't, sometimes short hop backward, or run away and pivot arcfire (this one works really well) etc. Avoid short hop forward ->arcfire because if you fail you may be punished by a charged smash.
When the guy grabs the ledge, you can spam arcfire right on the ledge, it's a pain to deal with this for some characters.
About the levin sword, use it each time you go for an aerial (don't think "I have only 25% chance to hit so I will save it for another time"). When it's broken, try to go for B moves and Nair instead of other aerials and avoid using smash attacks (Down smash is still decent without levin sword, and can still ko fairly early, but looses a lot of range. The 2 others are useless wihtout levin sword).
Abuse Uair, it's a godlike move. If there is someone under you, most of the time you want to fast fall Uair instead of Dair (unless you are want to spike him). Same thing if you are about to land right on your opponant, just fast fall Uair and try to land behind him (or BAir), Uair has way less landing lag than Dair.
The less you use nosferatu the better the move is (you have to surprise your opponant each time you use it). This move has a lot of end lag and is fairly slow, so if you use it too often and your opponant reads it, he will just dodge and destroy you. However, Nosferatu is really good when you try to land on a shield. It's also a good punish if you read a roll and you have more % than your opponant, otherwise just go for Dsmash.
Try to have an arcthunder ready at all time (or a thoron when your opponant is at 130%+). Arcthunder puts a lot of pressure on your opponant, because the projectile is really slow at the start. So it covers spot dodges, rolls, aerials, dash attacks...everything. The only thing your opponant can do are jumping over it, rolling behind you if he is really close or shield it. If he jumps, you can punish it with an Uair, or grab him when he lands. If he rolls, you should be able to hit an Ftilt before he hits you. If he shield, you can dash grab him. It's really scary to run on a robin whit an arcthunder ready to use. When you hit arcthunder, you can dash grab and get some free % on him.