Like the other Insular Celtic languages, Manx changes the first consonant of a word according to its grammatical environment. Manx has two such changes: lenition, a softening, and eclipsis, a nasalisation. They are not the same as the Irish ones, and applying Irish rules to Manx gets them wrong.
Try it
The main triggers
my “my” lenites: kayt a cat becomes my chayt my cat. nyn “our, your, their” eclipses: kayt becomes nyn gayt. Calling to someone lenites too: carrey friend becomes charrey!
The most useful pair is e. Masculine e “his” lenites; feminine e “her” does not, and instead prefixes an h to a word starting with a vowel: e habane her ankle. The mutation is the only thing telling the two apart.
Where the sources disagree
Two points are genuinely unsettled and the drill flags them rather than pretending otherwise. The spelling of lenited b and g varies between sources, though the sound does not. And on whether m and s eclipse, Wikipedia says they do not, while Old North gives m to p and s to t, which is not a plausible nasalisation and looks like a table error. We follow the first reading and say so.
Full sources on the Manx bibliography.