Variant Individual Speed (5e Variant Rule)
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This rule is designed to give variation in characters' speeds, while adding few mechanics (no new ability scores), and it produces less of an extreme effect than the other rule to this effect, meaning the speeds stay within more realistic ranges.
At the beginning of a creature's turn, it makes a Dexterity (Athletics) check. The result of this check determines by how much a character's speed is adjusted for that turn.
|Check Result||Speed Adjustment|
Creatures can become proficient in speed checks. Characters can get the proficiency via the skilled feat, or instead of a skill proficiency upon character creation. If they are proficient in both speed checks and Athletics checks, they add their proficiency bonus to the roll twice. If making a roll every turn is hard to manage, rolls can be made once at the beginning of a combat encounter, and used for the whole encounter.