JuliusBloodmoon said:
I think a Sea Serpent like monster (but would also be able to enter land squares) would be really cool
I have also thought a bit about this. Normally I don`t find the more advanced seafaring-techs too attractive to research. And why do I need +1 movement rate for naval units? War is commenced on land, and you only need ships to protect your ocean-recources.
So a barb sea-serpent that gurds a huge treasure, like the dragon, would be quite cool. It may also move and destroy fishing boats/ships, making naval exploration a lot more challenging...
The killer of the serpent might get a WW in his capitol (head of the sea-serpent?) granting perhaps a culture-bonus in every city, and a relation-bonus towards every other civ. Or a poison-promotion to all units built by the civ.
And inspired by Loke (I still don`t know about his ability to sire great wolwes, by the way

), Loke`s child Midgardsormen might be the model. Midgardsormen: Midgard=Middle-earth(Yes, Tolkien stole most of his ideas from Norse mythology) Orm(en) = (the) worm/snake/serpent
"Thor's fishing trip:
Another encounter came when Thor went fishing with the giant Hymir. The two did not get along, and when Hymir refused to provide Thor with bait, Thor struck the head off Hymir's largest ox to use as bait. They rowed to a point where Hymir often sat and caught flat fish, and he drew up two whales. Thor demanded to go farther, and so they did. Hymir told Thor that the part they were at was unsafe, because of the Serpent, but Thor ignored him, and to Hymir's horror they rowed out further.
Thor then prepared a strong line and a large hook, and Midgardsormen(Jörmungandr) bit. Thor pulled the serpent up; the two faced off, Midgardsormen(Jörmungandr )dribbling poison and blood. Hymir went pale with fear, and as Thor grabbed his hammer to kill the serpent, the giant cut the line, leaving the serpent to sink beneath the waves.
This encounter seems to have been the most popular motif in Norse pagan art. Four picture stones can be definitely linked with the myth.
Thor's foot goes through the boat as he struggles to pull up Jörmungandr in the Altuna picture stone.
The final battle
Their last meeting will come at Ragnarök, when Jörmungandr will drag himself from the Ocean and poison the skies. Thor will kill Jörmungandr and then walk nine steps before falling dead from the serpent's poison."