The pair's first international highlight was the 2014 World Cup Final in Lyon, where they finished 10th with 73.786%. Three months later Merkulova moved the 9-year old up to intenrational Grand Prix level at their home show in Moscow in June 2013. The pair made its international show debut at small tour level in March 2013 at the CDI Zhahskiv in the Ukraine. Originally owned by Russian entrepreneur and amateur rider Igor Goncharov, Mister X sold to Inessa (then Poturaeva) as a 5-year old. Merkulova commutes between her yard Ostehof in Bremervörde, Germany, and her stable in Moscow City, Russia.
The now 16-year old Mister X (by Egeus x Blank) got sidelined for two years because of a hoof injury and missed out on the planned 2019 World Cup Finals and 2019 European Championships, as well as were out of the running for Tokyo team selection.
After a two-year absence from the international show ring, Russian Inessa Merkulova returned to the arena with her beloved top ride, the Russian Trakehner Mister X at the 2020 CDI-W Minsk in Belarus on 16 - 18 October 2020.