鉴
=
刂
+
大
+
金
:
As Joan of Arc (ji) is looking at a bar of gold (金) in the anthill's bathroom (an4), she sees a reflection (鉴) of the robot (大) who wants to kill her with a kitchen knife (刂) and is warned (鉴) just in time.
于
=
亅
+
二
:
Mnemonic symbol: prepositions are what glue the sentence together. Honey is as sticky as glue, so I'll represent 于 by a honey jar.
Yu the Great was assigned to repair the electrics of the space station's entrance, but instead she was snacking some honey from a honey jar. Now her capacitor got stuck in the honey and she has to use a crowbar to lever it out.
(of time or place) in; at; on / (indicating any indirect relation) to; toward; vis-à-vis; with regard to; for / (indicating a source) from; out of / (used in comparison) than / (used in the passive voice) by