You want to hit them and double the rest of your damage for the turn, which can come from burn spells or from non first strike creatures that attacked alongside Lightning
Warriors Sword, The Prima Vista and token-making spells like Relms Sketching also count but saga creatures like Ramuh and Shiva wont, and neither will Travel the Overworld if you have more than three towns
Youll only get one per batch of creatures dying, but trust me when I say you dont want to play in a world where this red enchantment didnt have that floodgate in place
Honorable Mention: Initiative Cards The first room on The Undercity always fetches a basic land from your deck, which makes every card with the initiative a land-searcher of sorts
Lion Sash White decks have always been struggling in such a format like EDH, but fortunately, Wizards of the Coast have been regularly printing powerful white cards for commander in the last couple of years
In the vein of Oathkeeper, I also tossed in Nim Deathmantle which you can use to recur Raiyuu after he is destroyed if you spend four mana