This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鈯 combines 金 (metal) with 出, but the historical development and original meaning are uncertain.
The kanji has no clear meaning, so a mnemonic is not possible. Focus on its shape: metal 金 beside 出.
For トツ, imagine a metal tool that makes a sharp 'tots' sound when it strikes: tots -> トツ.