The dragon....Erathsmedor...ususally stays in the large field NE of Shurugeon castle, just South of the Dragon spire.
It could have been Swamp Muck...They attack, using a gas cloud....But....it Sounds like you just met the Amazonian Mantraps...aka the salads.
You might want to climb the wall of the castle and have a look around! You can easily get up on top....if you climb the broken wall...right where you came in. If they are nearby you'll see them. You
could run past them...but...They have a seek and destroy AI....They
Will...
Hunt you...Down!!!!!
There are a few tips in the Best tips, thread....on pages 1 and 6. AFAIK... Fire spells and fire bombs, work the best....especially if you can target them from the castle wall. I always did it the hard way. I beat them to death and died
Alot trying..