Someone set up us the bomb. Ten times over.
http://www.nintendoworldreport.com/news/74992/new-battle-mode-other-fixes-added-in-mario-kart-world-update
Mario Kart World has snuck an additional update in before the end of the fiscal year with a new battle mode and other changes.
The headlining option is the Bob-omb Blast option being added to Battle Mode. Players can hold up to 10 bombs and adjust the distance of thrown Bob-ombs depending on how long the L button is held down.
The full patch notes (found here) also detail adjustments to Bullet Bill and the Boomerang among other items, and resolved some issues with Mega Mushrooms.