Can I cast Arcane Shift without an enemy at a battlefield?

No, you cannot cast Arcane Shift without an enemy unit at a battlefield.

According to RiftJudge FAQ #378, Arcane Shift requires valid targets for both parts of the effect—a friendly unit to blink AND an enemy unit to deal 3 damage to—in order to be played on the chain. You cannot play it if there is no enemy unit at a battlefield.