BC2 strat guide (inspired by Rusty)

Bowser Castle 2 is an odd track. It's not nearly as optimization-heavy as the first Castle, though it can be equally as frustrating. If you're playing the tracks in order, it's the first track you will see a zipper without a ramp right by it. Hitting them are the keys to success here. Do note that this track has relatively easier standards than the previous 8 (which is why it starts at 1'08 as opposed to 1'10) although it is significantly more inconsistent compared to the previous 7 tracks.

High Advanced (~1'08) aka 2 Zipper
About 1/2 of a second after you boost start, hop into a right drift, trying to take the corner as tight as possible. You will slam into the wall a lot taking it tight, so get used to it. Actually get used to hitting every wall here, so you don't snap your GBA in half while grinding this. Once that's done, hit the first zipper. Just before the boost ends, hop into a left drift and release the MT once you're done. Navigate the next few turns as normal.
THE BUMPER FUCKFEST
This section gets its own header because fuck it, it does. You'll want to be hopping over every bumper you come by, and take the right path if possible. If you're already heading for the left path, don't bother going for the right path. DO NOT SHROOM HERE, THE BUMPERS WILL KILL YOUR SHROOM AND YOU WILL BE LEFT WONDERING WTF YOU ARE DOING.
Right, onto the next part.
Hang a drift onto the grates, the wall sticks out further than you think so expect to bump that a lot. Aim for the right path and hit that zipper, and hop over the 2 bumpers while you're at it. For the first bumper, you'll be wanting to hop left, and countersteer that just before the 2nd bumper comes up. Start a drift into the final turn, but shroom once your kart is no longer to the right of the little cavity.
Approximate Splits: 22"80-22"60-22"60=1'08"00 (Advanced B)

Lower Expert (~1'06) aka 3 Zipper
This is a lot of the same as the Advanced strategy, there's one catch. On the first grate section (before the bumper fuck fest), there's 2 zippers on either side of 3 bumpers. You'll want to be hitting either one. Start a drift earlier than usual into the grates, then countersteer. You should be lined up at it. A tiny bit after (no more than "2) after you hit it, start a right drift into the corner. Once the drift is finished, continue on the lap like the 2 zipper strat.
Approximate Splits: 22"20-22"05-22"05=1'06"30 (Expert D)

High Expert (sub 1'05) aka 4 Zipper
Once again, this is a lot of the same as the 3 zipper strat, except let's make it more frustrating because fuck you. After the 2nd zipper, you'll want to drift significantly earlier once you hit it. This will line you up for the 3rd zipper. Hit that then drift into the bumper fuckfest. Note that it is significantly harder to take the right path taking the third zipper, so if you have to take the left path it's OK. In addition, on laps 2 and 3, the thwomp just after it will be in your way, so adjust your line accordingly.
Approximate Splits: 21"65-21"55-21"55=1'04"75 (Expert A)

Mid-High Hero (~1'03)
This is a mere change in the shroomspot for this course. Instead of using it on the last turn, use it after the third zipper onto the bumper fuckfest. This will make taking the right path much easier, but makes the transition out of the zipper notably harder. If you want, charge and MT at the 2nd set of grates by drifting left then right.
Approximate splits: 21"20-21"05-21"05=1'03"30 (Hero B)

Flap
Releasing an MT into the lap is significantly harder than in the previous 7 tracks, due to there being a turn right after where you start, you have to do it significantly before the finish line in order for it to be optimal.
SHROOMSPOT 1(alternate)
This is a nice shroomspot if you cannot manage the one of the standard shroomspots, although it is less optimal (sub 20 is still very possible with it). Hop into the 2nd turn, and when you no longer have the chance of bumping the wall, shroom. You can either right hop to align yourself or release A and hold right until you round the corner.
SHROOMSPOT 1/2
This is the standard 3lap shroomspot, after you hit the third zipper (or as you round the corner if you're still doing 2 or 3 zipper strat), shroom over the bumper fuckfest. Note that this needs to be done immediately once you no longer have the chance of hitting the wall. Hop over all of the bumpers, (including the one leading to big boy lava) as shrooming into a BC bumper will kill your speed.
SHROOMSPOT 1/2(easy)
This is the same idea as the 3lap shroomspot, but you do it in the bumper fuckfest as opposed to just before. It's vastly inferior, but a lot easier as well.
SHROOMSPOT 2/3
After you hit the final zipper and its boost wears off, shroom. You will need to hop twice in order to avoid falling in the lava.
SHROOMSPOT 2/3(easy)
Same deal as 2/3, you just do it before the zipper. Not as useful but easier, as with 1/2(e)
SHROOMSPOT 3/4
This is the 3lap shroomspot up to hero level, simply round the corner and shroom when you no longer will hit the wall leading to the cavity.