My friend is playing Crystal and wants to know which legendary you can get in Crystal. He thinks it's Celebi but I think It's Scuicune because that's who's on the cover of the game.
You could probably only get Celebi through an event back in the day. You certainly won't be able to get it now (without cheating).
Suicune was part of the standard game along with Entei and Raikou so yes, you could catch it.
you get scuicune and i think celebii was an event pokemon years ago
Suicune,Entei,Raikou obviously but just because you can get them doesn't mean you will you could get your behind kicked for all you know.
If you are playing on the virtual console edition (from the 3ds eShop) you can get Scuine & Celebi in Crystal.