Surfs Up

You create a surf board, which has a flying of 60. The surf board has an AC equal to your spell save DC plus one, and has an amount of hp equal 8 times your spell cating modifier plus 10 times the level the spell was cast at. When its HP reaches zero, it shatters, destroying the material component, and ending the spell early. 

Additionally, anyone who rides this surf board temporarily gains an expendable energy known as Surfer's Spirit. The amount of surfer's spirit you get depends on the level you cast this spell at. When casting this spell at 4th level, you gain one surfer's spirit. When cast at 5th level, you gain 3 Surfer's Spirit. When cast at 6th level, you gain 5 Surfer's Spirit. When cast at a level of 7th of higher, you gain unlimited uses of Surfer's Spirit abilities, so long as you maintain concentration. When the spell ends, the user loses all Surfer's Spirit remaing, and the surfboard shrinks, or shatters if its hp reaches zero. Surfer's Spirit can be consumed to use the following abilities:

Surfing the Tides of Battle: Whenever you are hit with an attack, and that attack isn't critical, you are forced to make a Dexterity Saving Throw, or have to roll a Dexterity (Acrobatics) check, you may use your reaction and one Surfer's Spirit to roll a Dexterity (Surfing) check.

In the case of being hit with an attack, if your Dexterity (Surfing) check exceeds their attack roll, then their attack misses, and has a ten percent chance to hit your surfboard instead if the attack rolled were to hit your surf board.

In the case being forced to roll a Dexterity Saving Throw, before you roll your Saving Throw, you may roll a Dexterity (Surfing) check with advantage. The result of this is treated as though you had rolled that as a saving throw instead, and if it succeeds, you may move up to 15 feet in any direction as a part of this reaction. If you escape the radius of the attack, you take no damage. If you do not escape the radius of the attack, you take a quarter of the damage, while your surfboard also takes a quarter of the damage.

Board Block: When forced to make a Strength or Constitution saving throw, before you roll your Saving Throw, you may consume a use of Surfer's Spirit  to roll a Dexterity (Surfing) check. The result of this is treated as though you had rolled that as a saving throw instead, and if it succeeds, you may move up to 15 feet in any direction as a part of this reaction. If you escape the radius of the attack, you take no damage. If you do not escape the radius of the attack, you take a quarter of the damage, while your surfboard also takes a quarter of the damage.

Embodiment of Surfer's Spirit: When forced to make an Intelligence, Charisma, or Wisdom Saving Throw, you may expend a use of Surfer's Spirit to roll a Dexterity (Surfing) check at disadvantage. This roll replaces your saving throw, with no additional effects. You make this roll before you roll your saving throw, and do not roll the actual saving throw.

Wipeout:  As a bonus action, or as a reaction just before your surfboard shatters, you jettison your surfboard from under you. If you use this as a reaction, you may dive up to 30  feet towards the groung, so as to mitigate fall damage. After you use this, the spell ends. You roll a ranged spell attack at a creature within 120 feet of you. On a hit, the target takes 1d10 piercing damage plus 1d10 piercing damage for each Surfer's Spirit. If you have unlimited uses of Surfer's Spirit, it always deals 12d10.  Hit or miss, the board then explodes in an orb of water, leaving behind only wood splinters afterward. The target and each creature within 5 feet of it must succeed on a Dexterity saving throw or take 4d6 cold damage.