// context
void Room_killEntity(Room self, Entity entity)
{
    List_delete(self->entities, Room_getEntityIdx(self, entity), ((Entity)entity)->kill);
}

// only place it's called
    switch (e->type)
        {
        case SDL_QUIT:
        Room_kill(currentRoom, GAME_KILLED);
        SDL_Quit();
        exit(0);
        break;
            ....
// actual problem

void Room_kill(Room self, enum KillType kt)
{
    for (List cur = self->entities; cur; cur = cur->cdr)
    {
    if (cur && cur->car)
        Room_killEntity(self, (Entity)cur->car);
    }
    Sprite_kill(self->bg);
    // everything else is either autocollected or outlives us, so...
    free(self);
}