Can any better Faust players give me some tips?
First, work on your confirms. A CH j2K should be confirmable right there into Something > Pogo > Going My Way.
When defending against mixups in the corner, focus less on counterpoking and more on using Faultless Defense to make an opening for superjumping away. You can then cover your escape with Raw YRC, Bag Toss > YRC or YRC > Bag Toss to reset the game to neutral. Your far.S has a huge hurtbox on it, so it's liable to trade in a number of situations. You were counterpoking with 5HS as well, which just doesn't do the job as well as getting the fuck outta dodge.
If you want to counterpoke, use 5P to preemptively cover the space in front of you, then plan what comes after. 5P beats Mappa out of startup, which means you can cover Mappa, then block all of Slayer's slower followups when he does Dandy Step shenanigans. An example, after blocking Mappa from Slayer, I'll buffer 5P with 2D twice. This counterpokes Backdash Cancel Mappa to CH into 2D knockdown, and hits all of Slayer's other options outside of some loonier roundabout options (Of which I think you can cover with YRC on reaction) with the linked 2D after 5P recovery.
Have confidence in your Bomb explosion timing. I saw you landed a CH j2K on crouching Slayer with time to spare, which means you could have went for 5P,2D jump cancel for Bomb Combo. Always try gatling into 2S or 2D to get the jump cancel, you keep the opponent in pressure if they block, and you get sick damage if it connects. You can also jumpcancel a 2K or 5P if you want to squeeze in a hit.
At close range, don't go for cl.S xx Item Toss. If you're in range for cl.S, chain into 2HS/5HS xx Item Toss. It's safer on block, and if you find that it connects, you can forgo Item Toss for RC dash 2S,2HS xx Pogo xx Going My Way.
5D combo is supposed to be: 5D jHS jc jHS jc j.K,j.P,j.K jc j.K,j.S,j.HS
Be more brash when Meteors are out. You have no reason to avoid your opponent when Meteors are about to drop. You have Hidden Missiles. Just go in. Do unsafe things. HORRIBLY UNSAFE THINGS. Things like fucking awful Going My Ways and arbitrarily obvious jump-ins. You'll bait out a response from most players and still be at advantage if they don't fall for it.
Convert of CH 6P by always cancelling into Item Toss. This will allow you to get an Item into play while also following up with 5K jc j.K jc j.K,j.S,j.HS
When you get Spring Board off 2D, pressure your opponent with a properly timed j2K or 6HS. You'll be able to get unblockable damage off of it. You can practice it in Training Mode, and I recommend it as it happens so often.
Work on your punishes as well. All it takes is a little ogling of frame data to know what can be hit with a 5P,2S,2HS xx Pogo/Item Toss punish. Things like Slayer's Pilepunker should not go unpunished.
2HS is a great poke, despite it's slowness. At 25-49 meter, you can do 2HS xx 41236+K+S+HS to option-select a Scalpel Pull with YRC in case your opponent jumps over the 2HS. This is particularly important in some matchups where you can't react to their approach, and you can do similar things with 236+P+S+HS if you want to YRC OS with Item Toss as well. This is actually very useful if you land a far.S xx Item Toss againt Slayer, as the OS will beat all of his high-powered Dandy options at mid-range, while also Counter-hitting Mappa (At max-range 2HS OS xx Item/Scalpel is less useful and needs to be delayed slightly to catch his options)
Slayer's Helter Skelter (Hop into Stomp) can be punished on reaction with Dust YRC. Dust has invuln on startup, so you can use that to juke through moves with small amounts of active frames. Once you Dust YRC, anti-air him with 2K for an air combo.
If someone is hanging out in the air and pressing buttons (Slayer loves to do this with his j2K) look to j.HS at max range to beat it cleanly.
When you throw an Item that covers a certain part of the playfield (Bomb, Poison, Minifaust), you know that the only way out is going above or around the item in question. Use that to your advantage and stick a big fat j.S or j.HS in the way of your opponent preemptively. They can't approach on the ground, so you don't have to worry about them running in.
Bomb causes a hard floating juggle state, regardless of proration. This means if it lands, you always want to dash in 5K > Air Combo. It will always work.
Chaining into 2HS on block is sometimes better than 2D if you think they'll block. The reason being is 2HS leaves you at more advantage (Though blocked normals into Item are always minus).