You can better remember this character by noting that its pronunciation "dùn" is nearly the same as its meaning "ton".
Mnemonic
[du-] Dumbledore is in the [4] bathroom of the [-(e)n] infirmary trying to convince the nurses he is sick so that he can stay there. He shoves a magic 頁 page into his 口 mouth that he dipped in water from the sink, and seconds later begins to throw up a literal 噸 ton of half-digested 屯 earthworms all over the tile floor. The nurses then have to spend the next hour cleaning up the 噸 ton of 屯 earthworms as Dumbledore gets his 頁 page of admission and sleeps cozily on the tile floor.