Win yourself a new Arclight Rider Mount this week through gaining chests from completed quests in Moonshade Highlands. RiftGrate has an excellent guide. The only chance you have of getting the mount this week is through special Treasure Troves that you can earn from completing the event quests. The event quests also give you currency that you can eventually use to buy the mount outright from the PCI vendor, however it is not possible to earn enough in this week to do so. This will be like the other special promo-mount weeks (budgies, unicorns, etc.) that repeat every so often so you will have additional chances at currency to buy the mount.