不佳

This is how Henry Holiday imagined that the Boojum might look like:

How would Chinese call the Boojum?

• Boojum can be translated with 不佳 (bù jiā). The pronouncation in English is explained to Chinese people in fanyi.baidu.com.
• I also found 布经 (bù jīng) as a Chinese translation.
• As for vanishing away, one also could consider to use 不见 (bù jiàn).