When Selfless Squire enters the battlefield, its first ability triggers, preventing all damage that would be dealt to you this turn.
Cast Wheel of Misfortune by paying ({2} magic symbol) ({R} magic symbol) , choosing an arbitrarily large number, and preventing the damage it would deal to you due to Selfless Squire.
Selfless Squire's second ability triggers, putting a number of +1/+1 counters on it equal to the damage prevented.