When this creature enters, choose a letter. For each creature you control that has the chosen letter in its name, you gain 1 life and each opponent loses 1 life.
The chosen letter needn’t be in the English alphabet.
2022-10-07 • wotc
It doesn’t matter how many times the chosen letter appears in the creature’s name as long as it appears at least once. It’s 1 life per creature, not per letter.