Kin grunts as he hits the floor, the pain made worse by the hook of the halberd round his leg and the caltrops that pierce his skin. He skitters backwards, before a word and a gesture - while he is still prone - render him invisible to the naked eye.

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Kin takes a 5ft step towards J17 before casting Vanish on himself. I couldn't find anything in 5ft step or prone that said he couldn't take a five foot step while prone, so... if otherwise, I might have to rejig this turn again.