Dr. Kekyll's Grappling Framework

When you want to grab a creature or wrestle with it, you can use the Attack action to make a special melee attack, a grapple. If you’re able to make multiple attacks with the Attack action, this attack replaces one of them.

The target of your grapple must be no more than one size larger than you and must be within your reach. Using at least one free hand, you try to seize the target by making a grapple check instead of an attack roll: a Strength (Athletics) check contested by the target’s Strength (Athletics) or Dexterity (Acrobatics) check (the target chooses the ability to use automatically uses the higher of the two). If you succeed, you subject the target to the grappled condition (see below). The condition specifies the things that end it, and you can release the target whenever you like (no action required).

Escaping a Grapple: A grappled creature can use its action to escape. To do so, it must succeed on a Strength (Athletics) or Dexterity (Acrobatics) check contested by your Strength (Athletics) check.

Shoving a Grappled Creature: When you move, you can drag or carry the grappled creature with you, but your speed is halved, unless the creature is two or more sizes smaller than you.

Minor differences from RAW: Grappling an ally doesn't require a check, but ends automatically when their turn starts. This allows you to use part of your attack action to move an ally.

A grappled creature's speed becomes 0, and it can't benefit from any bonus to its speed. The condition ends if the grappler is incapacitated. The condition also ends if an effect removes the grappled creature from the reach of the grappler, such as when a creature is hurled away by the thunderwave spell.

I eventually plan to expand the logic for how NPCs decide whether or not to try to break your grapple, but there are a lot of AI Templates and the information I can pull to make the decision is limited at the moment.

A Note on Pinning (enabled by the Grappler feat): Technically, RAW, you both have the same r