In PvE, dragontail wont end the battle unless youre a lower level than it. So power levelling to anything above its spawn level, will work.
Alternatively, you can use a smeargle with the moves imprison, dragon tail, sweet scent and covet. Or do spore and covet and bring an additional sweet scenter. I recommend covet because with technician, its a decent single targeting attack move with stab (same type attack bonus) and has high PP to help make up for its ability to hit like a wet noodle in most cases