Synth a Slayers Bangle as shown in video. Synth a Scumbag Slayer with another Scumbag Slayer. Enter the Colosseum event "Bugs, Bugs, Bugs!" and start mashing A.
Edge gets about 1,000 hits per minute and Meracle lands about 600 per minute. This means that the trophy will take about 1.5-2 hours for Edge, and about 3-4 hours for Meracle assuming you started from 0 hits.