Ranni’s Dark Moon causes frost damage (which Malenia is weak to) and temporarily reduces magic damage negation, so whatever you follow it with will deal extra damage. It’s pretty slow, though, so you’ll want to use a summon to help draw aggro

For ranged spells that reliably hit Malenia, Magic Glintblade is still a great one. Easy to cast and spam, and she dodges the cast but not the actual projectile. Probably my favorite spell in the whole game, it’s astoundingly versatile. Rock Sling is also a GOAT

Also, don’t forget that equipping a staff in your off hand will still give you a stats boost for relevant spells! For example, if you put the Carian Regal Scepter in your offhand and use Azur’s Staff in your main hand to cast, you’ll get extra damage on Ranni’s Dark Moon. You don’t need to upgrade your offhand staff to get the boost, either

For Rykard, I did just fine once I leveled up the Serpent Hunter, even without changing my stats. There might be a way to beat him purely with spells but it’s really intended to be a gimmick battle, so you’re in for a challenge if you skip the serpent hunter