Cyclades
Can a fleet pushed by Polyphemus move onto the Kraken's space or onto an opponent's fleet?
No for an opponent's fleet, since its space is never a legal target. The Kraken's space is contested: the rule text says it is closed to fleets, but a forum reply relays Bruno Cathala saying you can push a fleet into it as a fun play (the fleet is then sunk). Players are split, so agree on it before play.