I've only seen this posted in one other place, so posting here: you can climb the first part of the waterfall in just a few tries by jumping out from dryness, and then doublejumping against the ledge and lining yourself right up for jumping up.
I've gone through the Large Cavern 15 times and haven't found an Alexandrite yet. Am I doing it wrong? I kill Jiang Shi a good 4-5 times for the EXP. I don't get how I'm getting some useless Minerva gear every single time.
If you want to find it faster, and are fine with less exp gain, try the Training Hall, you can find it there too. Once you get good at it, you can clear the Training Hall in 3-5 minutes with little trouble.
So far Ive gotten so many Super Potions and Super Tonics from the Training Hall, with a few Robe Decollettes as well. (Its mostly Super Potions, which are more useful at least), but only 1 Alexandrite. I still need 1 more so I can get a second Master Ring...
Edit: Could also buy it from the online shop, costs 24k to get though I think. Id sell it to you, but sadly my DS doesnt want to connect to the internet =/ May as well ask, how DO I connect? it said my access point isnt valid... --- The wheel of Fate is turning. Is it turning to your favor?