My question is if Chandra, the Firebrand's 2nd ability can effect cards cast with there Miracle cost. I'm pretty sure since planeswalker abilities can only be cast during the main phase like a sorcery then the player can't use Chandra's 2nd ability.
Correct and correct. A miracle is cast during the draw step, so Chandra can't be activated in time, but an instant like Increasing Vengeance (or Reverberate) can.
Now I believe a Miracle casted card can be copied with Increasing Vengeance.
UTeferi, Mage of ZhalfirU
xKarn, Silver Golemx
WUBRGSliver OverlordWUBRG
UBCircu, Dimir LobotomistUB
UMistform UltimusU
Thurn 1v1
Pauper EDH
Sage of Fables
Nivix Guildmage
Agent of Masks
Airdrop Condor
Imperious Perfect
Selesnya Guildmage
Orzhov Guildmage
Jund Battlemage
Standard
Modern
Booby Trap
Disciple Tinkets
UTeferi, Mage of ZhalfirU
xKarn, Silver Golemx
WUBRGSliver OverlordWUBRG
UBCircu, Dimir LobotomistUB
UMistform UltimusU
Thurn 1v1
Pauper EDH
Sage of Fables
Nivix Guildmage
Agent of Masks
Airdrop Condor
Imperious Perfect
Selesnya Guildmage
Orzhov Guildmage
Jund Battlemage
Standard
Modern
Booby Trap
Disciple Tinkets