Which Doraemon episode is this with Shizuka and multiple mini Doraemons? I have been looking for this episode for quite a while. I would appreciate anyone's help. Thank you.
The text on the upper-left reads 「大晦日だよ！ドラえもん」(Oomisoka dayo! Doraemon, "It's New Year's Eve!! Doraemon"), which is the title of the show.  
The subtitle reads「人類を救うために、ドラ・ザ・仮面登場！！」 (Jinrui wo sukuu tame ni, Dora The Kamen toujou!!, "To save mankind, Dora The Kamen appears!!).


This is from 2001's Doraemon New Year's Eve special episode, titled 「大晦日だよ！ドラえもん!!ミラクル大変身３時間スペシャル!!」 (Oomisoka dayo! Doraemon!! Miracle Daihenshin 3-jikan Special!!, "It's New Year's Eve! Doraemon!! Big Miracle Transformation 3-hour Special!!"). This special episode was broadcasted on 2001/12/31 from 18:00-20:54 JST and consists of 12 rerun episodes and 6 original bridging episodes:


ミニドラ救助隊 (Mini Dora Rescue Team) [Episode 1291]
冬眠シェルター (Hibernation Shelter) [Episode 1342]
ドラえもん　の　捕物帖 (Doraemon's Detective Story)
ジャイアンのディナーショー (Gian's Dinner Show) [Episode 1054]
ドラえもん　の　荒野のガンマン (Doraemon's Desert Gunman)
未来へのメッセージ (Message to the Future) [Episode 1247]
ドラえもん　の　黄門様 (Doraemon's Koumon-sama)
いつでもどこでもスケッチセット (Whenever, Wherever Sketch Set) [Episode 1053]
刑事　ドラえもん (Inspector Doraemon)
ママのありがたみ    (Mama's Blessing) [Episode 1077]
ジュラ紀でドラミが大ピンチ (Jurassic Age, Dorami in Big Trouble) [Episode 1489]
ボクを止めるのび太 (Nobita Who Stops Me) [Episode 1472]
ドラ・ザ・仮面 (Dora The Kamen)
カードテレビ電話 (Card TV Telephone) [Episode 1420]
特賞！のび太温泉 (Special Prize! Hot Spring Nobita) [Episode 1484]
名探偵　ドラえもん (Detective Doraemon)
雪だるまドラ太郎 (Snowman Dora-tarou)[Episode 1434]
白雪姫のリンゴ (Snow White's Apple) [Episode 1300]


Unfortunately, many Doraemon special episodes are only broadcasted on TV and don't have their home consumer version (DVD/BD), including this one.



References:


TV Drama DB (Japanese): Broadcast info
Hana Baloon (Japanese): Episodes info