For all the fighting Beelzebub does as a main card to earn her slot, she is mostly uncontestedly a great card as a sub. Similar to the color conditionals and Meiling, except only for attack cards, Beelzebub is incredibly flexible and offers a buff as a bonus for subbing her. Feel free to use her on any cards you can not find good subs for, or bite cards you don't have better subs for (or would desire enhanced stats over skill boost).
Her buff however is not reliable- After picking the stat to increase, it has approximately a 66% chance of applying the buff. But again, the main draw is the general boost, the buff is only a bonus.
