UndeadHalfOrc: Didn't take the tunnel to Castle Alamar (well I did, to take a quick peek, but quickly reloaded!)
There's actually a potential situation that could lead to a softlock (need Mr/ Wizard to escape), if you're playing MM5 alone. (You can do this by renaming a certain file; if you do this, the title screen will be different, and starting a new game will put you in Castleview with a level 5 party.) If you go into the Castle Alamar basement from the Darkside and cast Time Distortion (or perhaps even if you run from a battle), you will be teleported to the stairs to Shangri-La. Thing is, you can't get back to the rest of the floor if you haven't cleared it, and the stairs won't work without MM4 installed (some message about things not being in alignment or something), so you're stuck. Need to use Lloyd's Beacon, Town Portal, or Mr. Wizard to get out.
In MM4 alone, you can reach Shangri-La, but of course the stairs down from there won't work.
UndeadHalfOrc: Only thing left to do is the last room of the dragon cave with the dragon king. He obliterates me even with buffs.
So, you found that enemy to be more dangerous than the one at the end of Castle Xeen? At least the dragon can't eradicate your characters.
Edit: Well, MM5 *does* have a dragon that can eradicate your characters, but there's only 1, it's not required, and the game does give you a warning (plus teleport is necessary to reach it). It *is*, however, worth 100 million XP (good luck getting the money needed to gain those levels, if you're strong enough to actually win the fight) if you manage to defeat it. (If you somehow solo that particular dragon with a level 1-14 character, you will get enough XP to reach level 200 (the most you can ever train to) from that one kill.)