Hello IvanPP
You have regular trains from Basel to the station Ringsheim/Europa-Park and a bus shuttle to the Park in about 2 hours.
No special price is available with the Swiss Travel Pass. The price depends if you take only regional trains from Basel or an ICE to Freiburg and a regional train from this station. Please note that regional trains start usually in Basel Bad Bf and ICE in Basel SBB or other cities in Switzerland. Timetables and prices are already available on bahn.de, the STP is valid until the border station Basel Bad Bf.
Kind regards
Danhiel