Vizier of Tumbling Sands does not have summoning sickness.
You control a permanent that can tap to produce at least ({W} magic symbol) .
Illusionist's Bracers attached to Vizier of Tumbling Sands.
Steps
Activate a mana-producing permanent by tapping it, adding at least ({W} magic symbol) .
Activate Vizier of Tumbling Sands by tapping it, targeting Halo Fountain.
Illusionist's Bracers triggers, coping Vizier of Tumbling Sands' ability, targetting the mana-producing permanent.
Resolve both Vizier of Tumbling Sands abilities, untapping Halo Fountain and the mana-producing permanent.
Activate Halo Fountain's first ability by paying ({W} magic symbol) , tapping it and untapping Vizier of Tumbling Sands, creating a 1/1 Citizen creature token.