The event is basically summed up by the premise of "whoever does the most dmg wins the most rewards". Everyone starts off with 4 tickets, and any additional tickets come from winning player battles (i.e. knocking out all of the opposing rick's mortys), or buying them w/club rick tickets.
Thus far, the best strategy I've found (for battling the boss) utilizes strong accuracy/defense debuffs & stat-stacking mortys.
Reduce the boss' accuracy & defense first (2-3 times), then switch to a morty with a strong/medium defense & atk buff. Next stack each buff 2-3 times, then land as my attacks as possible. Scissor-types that can buff their atk & def are highly recommended (I personally use Cop Morty). Additionally, moves like Fan Art (or any poison-related attack) are relatively ineffective; since the boss is immune to poison. Lastly, use revives, plutonic rocks, and serums when necessary.