FTP, name this sibling of Hel and Fenrir that battles Thor to death at Ragnarok and is known to encircle the entire world.
A giant named Utgard-Loki asked Thor to lift his cat, but Thor couldn't as it was this creature in disguise.  Later, Thor went fishing for it with Hymir. They caught it, but it put up such a fight that Hymir panicked and cut it free.  At Ragnarok, the waves caused by it will set the ship Naglfar free. FTP, name this sibling of Hel and Fenrir that battles Thor to death at Ragnarok and is known to encircle the entire world.
A giant named Utgard-Loki asked Thor to lift his cat, but Thor couldn't as it was this creature in disguise.  
Midgard serpent or Jormungand