This is probably a really n00b question, but I honestly can't find the answer and I've been looking for a little while.

I know with the Main Shop discount buff, it only lasts for a certain amount of time. But does the 20 Percent Discount Card that can be purchased from the Cash Shop have a time limit before it wears off? Or is it just always there forever and ever--

I got one for Lumi and have been holding off on using it because I don't want it to wear off, but then again it seems like something purchased with CSC wouldn't do that, but I'm not sure. XD

It's there forever. Just make sure you lock it in your inventory, so you can't accidently delete or donate or zap it.

oh thank goodness. looks like it's going to join my lizard minion trap.

Ive got one, mines locked in my inventory too with my minion trap and spray, its very satisfying to see a little discount every time you buy something from an ncp shop, I havent saved tons of sp with it, but its still good especially as you got it as a gift, that was a great gift! and it works forever. I believe that if you have the spray and the trap it works better, but dont quote me.

The lizard minion spray + trap I believe gives you a 100% chance at getting the item but you can only get the comatose lizard achievement with the trap by itself

Also just for the record, the buff + discount card do stack but the wording on the buy page is kind of confusing

The spray and trap have no effect on the discount. Did you mean that the spray works better if you also have the trap?

Yes, the spray and trap give you a better chance of receiving the item mentioned in the lizard RE if you have both together.