Mask of Immolation doesn’t appear to function as its text indicates.
The card states that it deals 2 damage to the opponent whenever the first creature of Mask’s controller dies, but while using this card, losing my first creature (both token and nontoken) did not cause any damage to occur in at least 2 different cases, even when other supports with “whenever a creature you control dies” abilities triggered their effects correctly.
The first instance in which I observed this behavior occurred when a token created by Murder Investigation died due to Portal of Sanctuary’s “return to hand” effect (the token was my only creature in play, and therefore my first creature as well); Murder Investigation created another token and Moldervine Reclamation caused me to gain 3 life and draw a card, but Mask did not deal any damage to the opponent.
The second instance occurred when Abundant Maw (which was my first creature, with 2 Fleeting Elemental tokens as my second and only other creature) died to combat damage; again, Moldervine Reclamation caused me to gain 3 life and draw a card, but Mask dealt no damage to the opponent.