Spike Shell

You have 30-60 spikes on your shell.

With a DC 13 athletics check, another creature larger than you can throw/propel you at a target up to 20ft away dealing 1d4 + 1/4 of your AC. 

With a DC 15 athletics check, another creature larger than you can throw/propel you at a target up to 35 ft away dealing 1d4 + 1/4 of your AC + thrower's strength modifier. 

With a DC 20 athletics check, another creature larger than you can throw/propel you at a target up to 60 ft away dealing 1d6+ 1/4 of your AC + thrower's strength modifier. 

Upon a Melee attack that hits you, you may use your reaction to deal 1D4 + 1/4 of your AC to the creature that attacked.