Need help making CR11-13 Rust Monster

[GodPhoenix]

Any ideas on how to turn a rust monster into a CR11-13 encounter? What would be good templates to apply? I only have PHB, DMG, and MM1...so please explain ideas from other sources Thanks!

 

[Nifft]

6 rust monsters and 3 trolls? (CR ~10)

-- N

 

[Derulbaskul]

Here's a quick one:

advanced to 15 HD: CR 8
half-fiend template: +3 = CR 11

If you want to get really nasty and have access to other sources, slap the fiendish (MM), half-earth elemental (RttToEE? MotP?) and stony warrior (from FR's Underdark) on it making it the ultimate earth beast.

 

[Tyreus]

Advance it to 15 HD and give it the Monster of legend and ferel templates (CR 11). Now it gets good boost to stats, some specail abilities, and claw attacks. (as opposed to only the rusting touch)