@worldsendless Thats not a "character" in the unicode sense, that is an emoji. You can see all emoji by pressing the emoji icon in the text editor ont he web app.
@worldsendless they dont come with mastodon, well not all of them. You import them one by one in the admin interface. You can do this either by uploading a png and giving it an id, or you can see a list of all the emoji "seen" from other servers and just click a button to bring it to this server.. again one by one.
@freemo are those from a mastodon repo somewhere, or are they sourced from another library somewhere?