It is for competitive battling. It has a TIMID nature, 31 IVs in SpA, SpD, and Spe, and OUTSTANDING potential. I'd like an answer sooner rather than later so I can either save or give it up hopefully for 31 IVs in all except Attack. Thanks in advance!
Based on those stats, especially the Defence IV, I say reset it. Thundurus's No. 1 enemy is Landorus' Rock Slide, and for that you need as much Defence as possible. I suggest resetting, but if you're comfortable with where it is then keep it.