"There's one slight hitch: the jump required to reach the head is beyond Jekyll's capabilities. Go back down the stairs and climb the second floor on the other side of the room. Inside the accessible room (reddish-coloured lock) is a basin filled with water which, when mixed with the potion, will allow you to transform yourself into Hyde.
Having done so, go back down the stairs and go up to the second floor on the other side of the room. Right at the end, behind the last screen, you will find a medikit; you then need to kill the sniper, break the railing and gather enough momentum to be able to reach the head of the dragon from where you can exit the level. "
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Best wishes, Witchen =O)