No charge. The various performers on the cruise will do a family show early in the evening and an adult show later. There is usually a juggler, a ventriloquist, comedian, etc. Typically there are 4 variety acts on a 7 night Magic cruise.
The Right Stuff is the name of the live band currently on the Magic--again, they do sets in various locations around the ship at the scheduled times--no charge.
No charge for any of the entertainment venues on the ship...spa, bingo, tastings yes.
You do not normally miss the shows with late seating as they start like 10:30 or 10:45 (it varies over the years--check your Navigator) We did leave dinner once because we wanted to see a show...after several nights of talking to our head server about how S...L...O...W our server was. That night he was just worse than ever, and when 30 minutes after ordering dessert, it still wasn't there, we left. We also commented to the head server that we had things to do and couldn't spend over 2 hours each night to eat 2 courses! NORMALLY, dinner takes about 90 minutes unless your server is a real dud. You can hang out longer over dessert and coffee, but you don't have to!
As 3 Mickeys noted, dinner times vary too. Sometimes late is 8:15, sometimes it is 8:30...and a few years ago the start time depended on the rotation you were on. You will know what time your dinner starts when you board. The show times will be coordinated with the dinner times. Hakuna matata.