Damage Reduction and advancing a monster

[Mark Hoover]

If I advance a monster, in this instance a Mite, will its DR go up or scale at all as I add hit dice?

[Corbin Dallas]

By rule, the answer would be NO. There are ways to do it as the GM, some templates increase DR. Otherwise outside of this I think you would be in houserule territory.

[FLite]

I feel like if that is what you want, just add levels of barbarian (Invulnerable rager) to the mite instead of the advanced template. (besides, a raging barbarian mite would be hilarious.)

[Weirdo]

If you want to increase its DR, increase its DR. The monster advancement rules are more a guideline to the GM.

Just keep in mind a significant increase will increase the CR above the normal increase for HD. DR 5/cold iron is probably fine for a creature with a CR in the 1-3 range (Like the Atomie, Grig, Dryad, Redcap, Leprechaun, or Dryad).