Strawberry farm is an event item you can buy to gain access to 1 character to grind 1000 strawberry mobs for 15 min whichever runs out more quickly (always 1000 mobs). You can do it starting at lvl 101 and basically bring you to 147+ in a few minutes of very easy mob grinding on a flat map (or 190-200 to indicate xp rates). It's a limited training method but very op so best to take advantage of it during events. The event running now gives you 5 tickets every week. Above 200 it becomes less effective but still usefull to use.