How to convert them to *.ans format MysticBBS supports?
http://slackers.ddns.net/downloads.html
You can find all the best ANSi editors at the link above; I prefer Mobieus.
For converting from UTF-8 to ANSi, thats a toughy. However, anything that looks right (and is saved) using any of the ANSi editors at the above link, or saved using Mystic's built-in ANSi editor, will display thru Mystic correctly.
|07p|15AULIE|1142|07o
|08.........
--- Mystic BBS v1.12 A48 (Linux/64)
* Origin: 2o fOr beeRS bbs>>>20ForBeers.com:1337 (21:2/150)