Outside of availability, Orichalcum Pulse boosts the user's attack in harsh sunlight by about 33% and has some unique interactions with certain ability changing moves.
Orichalcum Pulse also boosts the Pokémon's Attack stat by roughly 33% (or more precisely, by a factor of 5461/4096) in harsh sunlight.
Skill Swap fails if either Pokémon has Orichalcum Pulse. Trace can copy Orichalcum Pulse. Role Play, Entrainment, and Doodle all fail when used on a target with Orichalcum Pulse. Orichalcum Pulse is affected by Simple Beam and Mummy.
Source.
And of course, as of Gen 9, both Drought and Orichalcum Pulse summon harsh sunlight upon switch in. Basically, Orichalcum Pulse is a better version of Drought for physical attackers.
Hope this helped!
