PS some additional info:

Ive had it for about a month, have watered it twice from the bottom and it was kept outside for a (somwhat cold and quite rainy) week before it was given to me.

That potting soil looks very rich and moist, and your plants leaves look like they are rotting.

So I think you may have watered it too much, or if not by watering too much, then at least your soil retains too much moisture.

You may want to observe and not let the plant get any worse or if it already is on its way to losing leaves, then go ahead and clip off the bad-looking (blackish) leaves. Do the same for any root or bottom stem/crown of the plant that may have been affected.

Get it into some new potting soil that is either bought at the store for succulent plants or mix your current stock of potting soil with equal parts sand, to make a faster draining medium for the plant to grow in.

You mentioned that you have an aloe and if the aloe hasn't had this kind of situation, then just treat this plant like your aloe.

Can't tell if it is Agave or Aloe, but it looks to be in dire straits. Being out in the cold for a week might have done it in before you even got it.

Pull it out of there and see what's rotted and what's not. Post some pictures and we can see if there's anything left to save.

I'd say it's a doner, sorry as that statement is. An Aloe, I think, that was loved too much.

This post was edited by cactusmcharris on Tue, Apr 15, 14 at 16:40

Thanks for the replies. Took it out of the pot earlier (actually, it almost fell out, as it was only covered by a cm of soil). Root was rotted through. There were about 3 healthy leaf tips that I've cut off just in case there's anything that can be done? I'm not holding my breath on that but thought it was worth a shot asking... It's a pity, as I was very much looking forward to watching/helping it grow and (hopefully!) bloom.

To the best of my knowledge, aloes don't grow from leaf cuttings, so I would toss those as well. If you get another one, put it in a porous mix...a minimum of 50/50 cactus mix and perlite. Never water a succulent/cactus after repotting...always wait about 5 days, then water thoroughly from the top until you see water draining out the bottom. Don't water again until the soil is dry. You can check that by inserting a pencil or skewer into the soil, much like inserting a toothpick into a cake.