Here is a useful strategy for the Grand Arena. Securing a victory does not always require you to possess Legendary cards. Because of the varying Contest rules, items of lower rarity are also fully capable of generating significant mXP for you. You can browse for these cards directly on the Ronin Marketplace using the address below.

http://marketplace.roninchain.com/collections/0x9e8ed4ff354bd11602255b3d8e1ed13a1bb26b4b