The following options give characters new alternatives to make use of their reactions during combat.

Guard: Palisade. If you take the Attack action during your turn, you can forego one of your attacks to stand guard and gain a bonus to your AC equal to half your Dexterity modifier (rounded down) until the start of your next turn. To do this, you must be unarmed or wielding a light or finesse weapon. If you’re attacked by a creature within your reach while you have your guard up, you can use your reaction to drop your guard and make an attack with advantage against that creature.

Guard: Phalanx. If you take the Attack action during your turn, you can forego one of your attacks to assume a phalanx formation and gain a bonus to your AC equal the number of allies within 5 feet of you until the start of your next turn. To do this, you must be wielding a shield. If you’re attacked by a creature within your reach while in phalanx formation, you can use your reaction to make an attack with disadvantage against that creature.

If any ally standing with you in the phalanx formation is attacked by a creature within its reach, they can use their reaction to make an attack with against that creature. If the attacker is within your reach, you can make an attack with disadvantage against it.

Guard: Steadfast. If you take the Attack action during your turn, you can forego one of your attacks to stand guard and gain a bonus to your AC equal to half your Strength modifier (rounded down) until the start of your next turn. To do this, you must be unarmed or be wielding a shield or a weapon that doesn’t have the finesse property. If you’re attacked by a creature within your reach while you have your guard up, you can use your reaction to make an attack with disadvantage against that creature.

Contrive. When you and an ally you can see are flanking a hostile creature, if your ally forces the creature to make a Strength or Dexterity check or saving throw, you can use your reaction to subtract half (rounded down) of your Strength or Dexterity modifier (your choice) from the creature's roll.

Trick Attack. When an ally that you can see that is flanking a hostile creature with you makes an attack against the flanked creature, you can use your reaction to make an attack against the flanked creature. Alternatively, if the flanked creature makes an attack against your ally, you can use your reaction to make an attack against the flanked creature.