难于登天

难 = 又 + 隹 : Mnemonic symbol: a video game which is almost impossible to beat.

难 = 又 + 隹 : Just inside the anthill's kitchen, Napoleon and a sparrow are trying to beat an insanely difficult video game. After playing and failing all day long Napoleon finally loses his temper and crashes the game wearing two boxing gloves.

于 = 亅 + 二 : Mnemonic symbol: prepositions (in, at, on, to, ...) are what glue the sentence together. Honey is as sticky as glue, so I'll represent 于 by a honey jar.

Yu the Great (于) was assigned to repair the electronics of the space station's kitchen (Ø2), but instead he was snacking honey from a honey jar (于). Unfortunately his capacitor (二) got stuck in the honey and now he has to use a crowbar (亅) to lever it out.

登 = 癶 + 豆 : To finance his adventures, Don Quixote (d) signed a sponsorship contract with a famous company producing canned beans (豆). In front of the engine ((e)ng1) he is scaling (登) a mountain of canned beans while wearing sexy nylons (癶). The character 登 depicts Don Quixote's legs (in nylons) standing on the mountain of canned beans.

天 = 一 + 大 : Mother Teresa (ti) programmed a robot (大) to play a flute duet together with her in front of the anthill (an1). As they play their flutes (一) an angel (天) hears their heavenly tune and descends from heaven to listen to them.