Instead of gaining proficiency in a new skill, you may gain expertise in a skill you're already proficient with, granting you advantage to all rolls with that skill.

If you are level 10 or higher, you may use a new skill to gain mastery in a skill for which you already have expertise. With mastery, you are assumed to succeed at all skill checks for which a roll of 15 or less would have been sufficient. You may still roll, if you wish; any d20 you roll lower than 10 is considered a 10 (unless it is a natural 1).

Some classes may grant skill alternatives, which allow you to spend a skill point to gain class-specific benefits. Refer to your class description.

Weapon skills are used to attack with weapons. Attacking with any weapon is a skill check. Those proficient with that skill gain their proficiency bonus to hit, as well as to damage rolls.

Any use of a weapon uses its associated skill check. For instance, a disarm check is a contest of weapon skill checks. There are some maneuvers and situations where a check might have advantage or disadvantage, but there are otherwise no modifiers to consider besides your proficiency bonus, ability bonus, and any equipment bonuses from magical or exceptional weapons.

Simple Weapons

Some weapons are "simple weapons". Everyone is proficient with these weapons. They use Dex if light, Str if heavy, and the wielder's choice if medium. Weapons that aren't simple are called "martial weapons" and are generally superior to simple weapons, but more limited in terms of which classes have proficiency in them (see table above).

Spellcraft is a skill used when casting any spell. If the spell is targeted, you use Spellcraft to determine the AC that you hit, and the DC of any saves to resist. If the spell is not targeted (such as an area attack), you still roll Spellcraft when attacking, and this determines the DC (if any).

:Note: this replaces the 5e core mechanics of "spellcasting ability modifier" and the formula for spell DC. Enemy minions are assumed to roll a 10 on all Spellcraft checks to set DCs.

Spells that are normally area effects can be targeted if you choose. To do so, choose a primary target. This target will be in the center of the area (center of a burst or square, middle of a cone or line). This is valid only if you can pinpoint the area effect; a close burst or emanation cannot be centered on a target, because it is centered on you. When centering an area effect spell, you roll Spellcraft to target the primary target, as if the spell were targeted. If you miss, you still hit the primary target with the area effect, so there is little disadvantage to using this option. The advantage is that you are able to critically hit the primary target on a natural 20, whereas area effects normally cannot cause critical damage;

It is not possible to invest skill points into Core Skills to gain expertise or mastery. However, all PCs whose class grants a given Core Skill gain benefits as they gain levels.

Weapon Skills

• Gain +1 die of damage with proficient weapon attacks at level 5, 10, 15, and 20.
• Thus, a medium weapon that does 1d8 damage at level 1 would inflict 2d8 damage at level 5, 3d8 at level 10, etc.
• This damage bonus is in addition to any equipment-based enhancements, such as magical enchantments.
• In 5e, fighting classes gain bonus attacks at level 5, 10, etc. This mechanic replaces that.