Tohar's Delayed Blast

You blow a small spark into existence, sending it to a point within range. Creatures or objects that move within 5 feet of the spark at any point during their turn trigger the spark to explode in a 10ft diameter sphere. Creatures must succeed a DEX saving throw or suffer 2d8 fire damage, or half as much on a successful save. Creatures that fail the save stop their movement and land prone 5ft back. The caster may manually dispel or detonate the spark as a bonus action