QUOTE
Playing a large number of rounds at lower difficulties in any battle mode reduces the drop rate from monsters for a period of time. This begins after 1,000 rounds and reaches maximum effect after 2,000 rounds. The reduction caps at 75% for Normal, 50% for Hard, and 25% for Nightmare. This applies to ALL drops besides Arena/Ring of Blood clear bonus drops. The round counter cools down at a rate of 1 per minute (out of combat only).
Hell以上の難易度にしとけば関係ないよ
それより下の難易度でもArena全部まわるくらいなら問題ないよ