Call of the World Serpent

You summon Jormungandr's Fragment (CR 15) . It appears in an unoccupied space that you can see within range. Jormungandr's Fragment disappears when it drops to 0 hit points, when the spell ends or when it uses its bonus action Summon Cancel. Jormungandr's Fragment is friendly to you and your companions for the duration of the summoning. Roll initiative for the fragment, which has its own turns. It obeys any verbal or telepathic commands that you issue to it (no action required by you). If you don't issue any commands to Jormungandr's Fragment, it defends itself from hostile creatures but otherwise takes no actions.

This spell can only be cast while wearing the "Bracelet of the World Serpent" because its the item containing the fragment of Jormungandr's soul required for the spell. The bracelet also has a self defence function that activates the spell when the caster falls unconscious: during this time Jormungandr's Fragment acts only to protect its summoner and itself and if the summoning ends in any way before the summoner wakes up then the soul's resting time is 10 Minutes.

Jormungandr's Fragment is a piece of the real World Serpent's soul materialized in a physical form, because of this, every time it dies, its body disappears and the soul returns to the bracelet in which it resides. Every time the soul returns to the bracelet it needs time to rest: if the summoning was cancelled with the bonus action Summon Cancel then the resting time is 30 Minutes; if the summoning was cancelled by the time limit then the resting time is 1 Hour; if the summoning was cancelled by Jormungandr's Fragment's death then the resting time is 3 Hours.

Even if it's just a small fragment of a soul, the original jormungandr is still a godly being. this means that Jormungandr's Fragment possesses intelligence on par or superior to a human and conserves all the memories of every time it was summoned. This does not contradict with it following all of the summoners commands.