Call the Leviathan

You call upon the power of the sea drake to surround you and carry you into battle. A large amount of water surrounds you and forms into a dragon-like body. Whilst the spell lasts, you are under the following effects:

• You gain temporary hitpoints equal to 2x your level. 
• Your size becomes Large, and your AC drops to 15. 
• You gain a flying and swimming speed of 100 ft..
• You are resistant to fire, poison and acid damage, as well as non-magical piercing, bludgeoning and slashing damage. 
• You are immune to the prone, grappled, poisoned and restrained conditions. 
• You are vulnerable to force and lightning damage, and if you take cold damage, your speed is dropped by 20ft until the end of your next turn

Whilst in this from you may take the following actions on your turn - 1 Flyby movement and 1 Bite attack.  

• Flyby - As part of your move action you may decide to fly into and through a number of creatures equal to your Charisma modifier. Any creature you fly into/through must make a Strength saving throw, taking 2d8 bludgeoning damage on a failed save and half that on a successful one. Any creature of size Large or smaller that fails the save is also knocked prone. Huge or large creatures cannot be knocked prone in this manner and count as difficult terrain when flying through them. 
• Swallow - You may attempt to bite and swallow a nearby creature. Make a melee spell attack against a creature within 10ft of you. On a hit, the creature takes 4d8 bludgeoning damage and must succeed on a Strength saving throw or be swallowed. Whilst swallowed, the creature is restrained and cannot breathe, and is carried by you when/if you move. At the beginning of each of the creatures turns the creatures can attempt a Strength saving throw, pushing itself 5 ft outside of the drakes body on a success. This attack can be done at any point before, during or after your movement, and only one creature may be swallowed a time.