the most common Fire types, Typhlosion and Magmortar, are Specs/Scarf, respectively. that means that Relicanth can come in, take the Flamethrower, Rock Polish up and sweep.
please think before you make comments.
And yet, Typhlosion (and other scarf Fire types) with HP Grass or Thunderbolt (common) can just switch back in after you kill something / your opponent sacs a low health Pokemon, outspeed, and KO Relicanth. The tactic does not work as well as you would think.