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 [1] front of the [-(e)n] infirmary where he is helping the nurses and doctors tend to the infirmary garden. He uses his magic wand to dig up a 吨 ton of soil that he piles on the grass lawn. Him and the nurses go through the 吨 ton of soil to pick out a bunch of 屯 earthworms, putting some in their 口 mouth as an idle snack. These are magic 屯 earthworms that can act as vaccines, and their goal is to collect a 吨 ton of 屯 earthworms to give to all current and future patients.