Bob-omb Blast is the Mario Kart World Battle Mode added after launch for last-player-standing matches. Its objective is to eliminate opponents until only one player remains.
Mario Kart World launched with returning Battle Mode activities including Balloon Battle and Coin Runners. Bob-omb Blast expanded that selection in a later free update, giving players a battle centered on explosive elimination rather than balloon popping or coin collection.
The name can be confused with Knockout Tour because both involve eliminating competitors. They are different modes: Knockout Tour is a long racing event with checkpoint eliminations, while Bob-omb Blast is a Battle Mode activity in which players fight for survival in an arena-style contest.