She will be played in standard, she can come down on turn 5 most of the time or even try for a turn 4 drop maybe.
If you get a turn 4 7/7 flyer with her abilities it can be game ending in a blue white skies deck running spark double for fun.
Let's not forget M20, has a 3 mana flyer that makes another flying token when etbs.
So you need a first turn flyer, second turn flyer 3rd turn cast the guy with the token, that's 4 creatures. Fourth turn you can tap then to cast her, or even cast another one or two drop if some of the others die, and then tap them to get her out.
Paradox Engine along with 4 flyers and a sacrifice outlet for Sephara, Sky's Blade as your commander with a non-land mana source to pay W is infinite ETBs.
If you can produce more than W then you can of course get infinite mana. Gilded Lotus or Coveted Jewel can help with that
Niv-Mizzet Reborn
Feather, the Redeemed
Estrid, the Masked
Teshar
Tymna/Ravos
Najeela, Blade-Blossom
Firesong & Sunspeaker
Zur the Enchanter
Lazav, the Multifarious
Ishai+Reyhan
Click images for decks->
-Prime Speaker Vannifar
---------------------Will & Rowan Kenrith
If you can produce more than W then you can of course get infinite mana. Gilded Lotus or Coveted Jewel can help with that
Blasting Station
Ashnod's Altar
Phyrexian Altar
Fanatical Devotion
Martyr's Cause
Niv-Mizzet Reborn
Feather, the Redeemed
Estrid, the Masked
Teshar
Tymna/Ravos
Najeela, Blade-Blossom
Firesong & Sunspeaker
Zur the Enchanter
Lazav, the Multifarious
Ishai+Reyhan
Click images for decks->
-Prime Speaker Vannifar
---------------------Will & Rowan Kenrith