Trident Mastery

You've immersed yourself in training with your trident, becoming an expert in its use.  After countless hours, blood, tears, and sweat, you gain the following properties:

• While wielding your weapon, it gains the finesse property if it does not already have it.
• You gain +1 to your AC while wielding your weapon one-handed if it has the versatile property (this stacks atop other bonuses).
• When thrown, your weapon deals +1 die damage (1d6 becomes 1d8, 1d8 becomes 1d10).
• Every four character levels spent training and using your weapon, it increasingly deals greater amounts of damage (every four levels, the damage die increases by 1: 1d6 becomes 1d8, 1d8 becomes 1d10, 1d10 -> 1d12, 1d12 -> 2d8, 2d8 -> 2d10).