1. Flanking
- have two melee or ranged attackers on exact opposite sides of an opponent, and this works for opponents too.

2. Grappling
- upon successful grapple, you gain advantage on close range attacks and they will have disavantage on attacks. However an additional attacker if attack roll is 1 on either advantage rolls, they will hit the grappler. If it's a 1 and 20 roll it will hit but no double damage.

Other standard rules to these apply.