In our Spelljammer campaign, my players have learned the joys of casting Enlarge on the ranger/paladin. Thinking through his significant increase in size and weight, he decided he should be able to jump on a prone enemy and do significant damage. I had to improvise a roll on the spot for it that time, but I have no doubt this will become a recurring tactic, perhaps even our own answer to the Fastball Special.
So, below is the current version of the rules we’re playtesting. The calculations are pretty simple and derived from the Dungeon Master’s Guide section and improvising damage.
These rules are for when an attacker wants to jump and stomp on a prone or otherwise circumstantially justifiable target. It is necessary for the attacker to be able to use gravity to differentiate this attack from a standard unarmed strike.
The following table is derived from DMG’s Damage Severity and Level table. All rolls are measured in hit dice so that damage is proportionate to the general trends of the attacker’s class.
| Character level | Target is same size as attacker | Target is one size smaller than attacker | Target is two sizes smaller than attacker |
| 1st-4th | 1HD | 2HD | 4HD |
| 5th-10th | 2HD | 4HD | 10HD |
| 11th-16th | 4HD | 10HD | 18HD |
| 17th-20th | 10HD | 18HD | 24HD |
If the difference in size is three or more, consider it an instant kill.
If the attacker is one size smaller than the target, the damage is half of the roll of a single hit die regardless of level. If the attacker is more than one size smaller than the target, it has no effect.
If the target is able to make a dex save, the target attempts a dex save with a DC 15 to reduce the received damage by half. (In this case, the target is effectively rolling with the blow, causing the attacker to slide through the stomp rather than come down their full weight on the target.)