Thanks to Nick Denmark/Poland's new leak and Thumpleaf's plot leak for a episodes, Here's the list of every season 12 episode.
Most of these came from the Nickelodeon Denmark sitemap. (nickelodeon.dk/sitemap.xml.gz)
242a - FarmerBob
242b - Gary and Spot
243a - The Nitwitting
243b - The Ballad of Filthy Muck
244a - The Krusty Slammer
244b - Pineapple RV
245a - Gary's Got Legs
245b - King Plankton
246a - Plankton's Old Chum
246b - Stormy Weather
247a - Swamp Mates
247b - One Trick Sponge
248a - The Krusty Bucket
248b - Squid's On A Bus
249a - Sandy's Nutty Nieces
249b - Insecurity Guards
250a - Broken Alarm
250b - Karen's Baby
251a - Shell Games
251b - Senior Discount
252a - Mind the Gap
252b - Dirty Bubble Returns
253a - Jolly Lodgers
253b - Biddy Sitting - SpongeBob and Patrick get tricked into babysitting a grouchy old lady, who does all she can to escape.
254/255 - SpongeBob's Big Birthday Blowout
256a - SpongeBob in Randomland
256b - SpongeBob's Bad Habit
257a - Handemonium
257b - Breakin'
258a - Boss for a Day
258b - The Goofy Newbie
259a - My Two Krabses - Mr. Krabs gets ready for hot date, but SpongeBob and Patrick give him a little more help than he needs.
259b - The Ghost of Plankton - Plankton becomes a ghost to steal the secret formula, but requires a few lessons from the Flying Dutchman.
260a - Knock Knock. Who's There?
260b - Pat Hearts Squid
261a - Lighthouse Louie
261b - Hiccup Plague - No one in Bikini Bottom is safe from a case of contagious hiccups.
262a - A Cabin in the Kelp
262b - The Hankering
263a - The Kwarantined Krab
263b - Kooky Cooks
264a - Plankton's Intern
264b - Patrick's Tantrum
265a - Bubble Bass's Tab
265b - Who R Zoo?
266 - Escape From Glove World
267a - A Place for Pets
267b - (unknown because sitemap said this was a duplicate) Possibly: Pineapple Panic - The citizens of Bikini Bottom panic when SpongeBob's pineapple begins to grow over the entire town!