FormerlyHemlock
Hero
Good post Arial. I have to nitpick though:
He can still shield bash as an attack, which means he can probably Push enemies prone (which knocks flying enemies out of the sky) or aside (which knocks enemies off the ladder, although Shove Aside is done at disadvantage per DMG rules). On a ladder that's actually probably a better move than a regular longsword attack, if your enemies are on ladders too. Or you could just attack with your shield as an improvised weapon for 1d4+STR. Failing that, you can head-butt for 1 + STR. But Pushing is probably the best choice.
If he has to climb a ladder, impose penalties for using only one arm and make it almost impossible to climb a steep ladder with no hands. He then has to choose to put both sword and shield away, or choose only one of them to keep in hand. Weapons can be drawn as a free interaction, but donning/doffing a shield takes your action. Attack him as he climbs. If he only keeps his shield then he cannot attack back.
He can still shield bash as an attack, which means he can probably Push enemies prone (which knocks flying enemies out of the sky) or aside (which knocks enemies off the ladder, although Shove Aside is done at disadvantage per DMG rules). On a ladder that's actually probably a better move than a regular longsword attack, if your enemies are on ladders too. Or you could just attack with your shield as an improvised weapon for 1d4+STR. Failing that, you can head-butt for 1 + STR. But Pushing is probably the best choice.