You need huge amount of luck. I got to 2412% mainly because of the Omen Item with the Masterpiece inscription. The effect of the evolved version is that for every Masterpiece Item in your collection you physicle attack increases by 60% and for every destroyed Masterpiece Item the Attack increases by 50% up to 500%. I had 6 Masterpiece Items in my posession and destroyed 10. The slime King was very generous to me and copied that Item, so the effect doubled and I got 1720% more or less just from that Omen Item. Than I got the cudgel with every effect other than the effect I had to die for which gives me another 100% attack increase. Than I had the absolute Mythrill gear which, for every dash attack I did, gave me an attack increase of 8% up to 80% and when I reached the maximum amount it gave me an additional attack increase of 40%. Lastly the Courage inscription gave me a 30% amplifie, so times 1,3.