I’m interested in getting a Sandygast to go along with the ghost-type pokemon I have so far. What do I need to get to make it a suitable living condition in my house?

Luckily, sandygast are extremely easy to care for. At the very minimum, they need a sizable sand pit to rest in (even a large sandbox will do). They don’t need to be fed, but some may still enjoy it, so offer food only if it sounds interesting to your sandygast. Change the sand every so often (regardless of whether or not you feed it) to clear out any waste products, and provide a few toys it can move without needing to move itself from its spot too much. Finally, always, always keep it dry during the rain; otherwise, it will become waterlogged and sluggish (at best) or unstable (at worst). Keeping it indoors at all times may be a good idea, but if this isn’t possible, simply ensuring that its sandbox is covered before the rain hits should be sufficient.