Well, if a Spellcard misses then you're certainly doing it wrong. I doubt anyone would fire a Master Spark without assuring that it will land.
Anyway,
I made a cheapass, lazy combo for Marisa. Pardon the video quality. Probably due to wrong settings
Not quite a 10k, but close, and arguably the easiest one I've did. Maybe possible with piano, but I'm still not used with it.
However, the point of that video is to show how cheap Marisa's 4C is.
It has very high proration (a measly 5% reduce), NO stun rate, and you can chain it up to 5 times by timing the button presses. Though 4 is enough, since you need 1 spirit gauge for your follow-up BnB combos. It also connects from a jA, though spamming the 4C too much will limit the enemy after the j2A, so no MS.