Alexander Card - FF8 Guide
Location: Lunar Base/Southern Esthar Area
Card Mod: 3 Moon Curtains
First Available: Disc 3
The Alexander Card is won from Piet on the Lunar Base later on during Disc 3. Lunar Base uses terrible rules so it's a really difficult card to win, but with enough patience and perseverance you can do it. It'll actually be easier to win this card when you leave the Lunar Base and you visit Piet back at the crash site (pictured below).
For this card as well as any other card that you have to win with the "Direct" Trade Rule, the best advice I can give to you is use a set of Level 5 monster cards with maybe one or two Level 7 Boss Cards. This way incase you win the card you're after but still lose some cards in the process, what you lost isn't irreplaceable. This will save you many resets in the long run.
If you Card Mod the Alexander Card you'll receive 3 Moon Curtain items which can be used to teach a GF the Auto-Shell Ability. You could also turn each of the Moon Curtains into Shell Magic by using (Supt Mag-RF) but I don't recommend you do that at all.
Out of all the GFs there's only one that learns the Auto-Shell ability naturally, Doomtrain. If you'd like to make the most out of the Moon Curtains you get, I would recommend using them on a GF that is not typically paired with this GF. Here are some of your options...
GFs to teach Auto-Shell to: Tonberry, Cactuar, Brothers, Leviathan