Weapon (halberd), rare
When you roll a 20 on your attack roll with this magic weapon, the target takes an extra 7 damage of the weapon’s type.
Proficiency with a halberd allows you to add your proficiency bonus to the attack roll for any attack you make with it.
Notes: Damage: Additional, Damage, Combat, Heavy, Reach, Two-Handed
7 more damage in a critical is weak for a rare weapon.
Even if you are a Champion Fighter, there is a 10% chance to deal a critical hit. In every attack you have +0.7 extra damage.
If you use a +2 magic weapon (rary) and you can hit your target with 11 in a D20 roll, you have 50% chance to hit. So, this is a +1.0 extra damage (and +10% to hit, because the +2 to attack).