the only way is to use a gameshrak or trade from firered/leafgreen
First you need a magmar leafgreen and Pokemon xd gale of darkness can get magmar trade magmar to ruby then breed it hatch the egg to receive magby.
Catch It In Cinnabar Island
You can't get one at all in Ruby. You'll have to trade one from FireRed/LeafGreen.
you must trade or migrate a magmar/magby from another DS Pokemon game or Pokemon ruby/sapp etc trade a magmar while it is holding a magmarizer for it to evolve into a magmortar
Enter a contest, help the Pokemon from Aquare/Magmar and stuff like that.
Magmar doesn't evolve in Pokemon Red, Blue, Yellow, Green, Silver, Gold, Crystal, Ruby, Sapphire, Emerald, FireRed, or GreenLeaf. It can only evolve in the newer Pokemon games.
I assume you mean is Magby in Ruby, the answer is no since Magby/Magmar can only be found in Leaf Green or Pokemon XD
You can't catch a Magmar in Ruby or Sapphire just in LeafGreen.
No only leafgreen can get magmar.
Magmar can only be caught in Pokemon LeafGreen, therefore, you have to trade.
Magmar is a Pokemon exclusive to leafgreen so no you can't get it.
when it is held by magmar, and then magmar is traded, magmar will evolve into magmortar