Vedalken Mastermind | Intruder Alarm | Dual Nature

(and two other cards)

Cast
Phyrexian Walker by paying ({0} magic symbol) .
When
Phyrexian Walker enters the battlefield,
Intruder Alarm and
Dual Nature's first ability triggers.
Resolve the
Intruder Alarm trigger, untapping all creatures.
Resolve the
Dual Nature trigger, creating a token copy of
Phyrexian Walker.
Activate
Phyrexian Altar by sacrificing the
Phyrexian Walker token, adding ({U} magic symbol) .
Activate
Vedalken Mastermind by paying ({U} magic symbol) and tapping it, returning
Phyrexian Walker to your hand from the battlefield.
Dual Nature's second ability triggers, exiling nothing.
Repeat.