Alvin controls a Loyal Pegasus and a Traveling Philosopher. During his attack step, Norman targets the Pegasus with the activated ability of a Shipwreck Singer. Is Alvin forced to attack with both of his creatures?

When declaring an attack, you need to fulfill as many requirements as possible without violating any restrictions. By attacking with the Pegasus and the Philosopher, you're fulfilling all requirements (and not violating any restrictions), so you will be required to attack with both the Pegasus and the Philosopher. You cannot choose to not attack, since that won't maximize the number of requirements that you could fulfill, and you can't just attack with the Pegasus since the Pegasus cannot attack alone.

Nathan Long
Wizards.Com Boards NetRep

Follow-up, just so everyone understands (and so I can confirm my understanding!)…

Same scenario as before, but Norman also controls Ghostly Prison; my understanding is that the game can't force Alvin to pay mana, so the Prison's restriction prevents meeting the requirement?

Slight variant on the original scenario: Alvin controls Loyal Pegasus and Floodtide Serpent, and at least one enchantment; Norman uses Shipwreck Singer to force Loyal Pegasus to attack. Does Alvin have to return an enchantment and attack with both?

Thanks in advance!

That's actually covered by the last sentence of 508.1d:

508.1d The active player checks each creature he or she controls to see whether it’s affected by any requirements (effects that say a creature must attack, or that it must attack if some condition is met). If the number of requirements that are being obeyed is fewer than the maximum possible number of requirements that could be obeyed without disobeying any restrictions, the declaration of attackers is illegal. If a creature can’t attack unless a player pays a cost, that player is not required to pay that cost, even if attacking with that creature would increase the number of requirements being obeyed.

If there's some additional cost to attacking, you're not required to pay it even if paying it increases the number of requirements that are being obeyed. So you would not be required to pay 2 to pay the Prison tax, and you would not be required to bounce an enchantment to enable the Serpent to attack.

Nathan Long
Wizards.Com Boards NetRep