these two offer little to zero defensively (rilla checks stuff with priority and nido only counters koko) + nido can't switch into anything else, so you need very good role compression and momentum to support them.
ironwater pretty much laid out the flaws of the core, so I feel like I only need to add suggestions and ideas.

is the first pokèmon that comes to mind to support the core: by itself it can somewhat check kyurem, tapu lele, opposing rillaboom and weavile, while also providing momentum and potentially knock off or - as a last resort - defog support. pretty much everything that would switch into scizor gets clapped by nidoking so that's fun.

while it adds up ice weakness, it also brings to the table momentum, knock off support, defog and the ability to softcheck many fast threats that give the core trouble.

gives appreciated speed control and knock off + loves grassy terrain + nice secondary electric immunity.

if you really want to destroy your opponent with sheer damage. it works well with zeraora also because it allows zera to run volt switch because lando is caught in two minds (block the volt switch or gift g-zap a kill) and will hesitate to switch into it. also everything that zera lures gets in clapped by nidoking. gzap can also put pressure on shared checks to rilla like kanto zap while murking bulky grasses and buzzwole which rilla hates.
hazards setters with good matchups against defoggers (meteor beam

/ smack down sd

/

). allow you to keep rocks up for augmented damage output. av torn especially threatens nidoking but can drop into +2 or cb glide range thanks to rocks.

gives speed control, reliable pivoting and a check to stuff like gzap and tornadus-t.

gives defensive backup, defog and uturn, role compression here as well
in all honesty, I don't particularly like the core because it puts a massive strain on the rest of your team and it's bound to leave you exposed. teams like these can work but rely on offensive prowess A LOT more reliable than nido+rilla. they are pivoted, resisted and outsped by 3/4 of the meta at least. that being said, if you like the core you can try and those were my suggestions. most importantly, have fun!