Definition
The Prone condition positions a humanoid character horizontally across the ground, either on their front, back or side. This condition has a mixture of benefits and weaknesses and alters the character's movement options.
Trigger
A character can become prone in two ways, willingly or by force. Willingly A character can go prone in one action frame, shifting from a Crouch and then finally into the prone condition. If the character dives or otherwise skips crouching, this still takes a frame to land prone on level ground and an additional frame for every 10ft fallen. Going prone in such a forceful way can cause a character to become Staggered for a split-frame, meaning the character will only manage to get back to a crouching stance by the end of their action frame and be unable to move during the Stand-Up activity. By Force A character can be knocked down or otherwise forcibly repositioned by an effect or attack. If a character lands forcibly they may be Staggered and unable to get up or move for one frame. Quite often, the character will be Prone if they fail a Saving Throw to avoid falling over.
Effect
When a character is Prone, their movement speed is drastically reduced unless they have an ability or modifier to move differently whilst crawling or prone. The movement type of a prone character is a Crawl in this state. Crawl Speed A character's crawl speed is usually half the character's base speed rounded down. Should a character's speed be reduced to 0 in this state, their speed is instead 5ft over two Action frames. Crouch Stance A character who is Crouching can move their base speed minus 5ft each action frame. While crouched the character doesn't lose advantage from attacking but may have to automatically stance/uncrouch to do so. Attackers lose advantage to hit from range, but penalties or advantages for attacking in melee. Melee and Ranged Attacks Attackers gain Advantage against the prone character within melee range of the attacker, and suffer Disadvantage for any attacks beyond melee range. Attacking while Prone A character can still perform activities and attacks even while prone, but only if the attack form or ability support it. Melee attacks lose Advantage, but ranged attacks can be used without penalty providing the user is at least an Expert in their attack form, and/or doesn't disrupt their ability to aiming and fire.
Stand Up Activity
Characters can stand up in the same square as they were prone as an activity during one action frame. A character only needs a split-frame to gain a crouched stance so they can move an additional 5ft in any direction provided their speed is greater than 5ft. A character can also get up while having one grasping appendages occupied (by interaction or holding something), however not using the minimum amount of limbs will extend the time to stand up to a full frame and disallow movement.