While you have more attackers than Fitri has blockers, your creatures alone won’t be enough to take her down. That Friendly Fire in your hand can do the rest of the work, but you have a couple of obstacles to overcome: First, you can’t target any of Fitri’s creatures. Second, Fitri has no cards in her hand.

That said, no one said that winning the game was easy. You just have to put in a little work…

1. Tap two plains to add (one used as generic mana) to your mana pool.
2. Spend to cast Abzan Advantage, targeting yourself. This forces you to sacrifice an enchantment; sacrifice the Jeskai Runemark. Abzan Advantage then lets you put a +1/+1 counter on a creature you control with the lowest toughness; choose to place this on Mardu Scout. Mardu Scout is now a 4/2 creature.
3. Declare the start of your combat phase. Tap a mountain to add to your mana pool.
4. Since you now control a creature with power 4 or greater, spend to activate Flamewake Phoenix’s ability, returning it from your graveyard to the battlefield.
5. Assign your Mardu Scout (4/2), Arashin Cleric (1/3), and Flamewake Phoenix (2/2) to attack.
6. Fitri may block one of your attacking creatures. If Fitri blocks any creature:
   1. Fitri may take the least amount of damage by blocking the Mardu Scout, in which case your creatures will deal a minimum total of 3 damage to her. Fitri is now at 5 life. Any creature blocked by Silumgar dies.
   2. On your second main phase, tap two plains to add (both used as generic mana), one island to add , and two mountains to add (one used as generic mana) to your mana pool.
   3. Spend and exile four cards from your graveyard (Frost Walker, Abzan Advantage, Jeskai Runemark, and the creature that died during your combat phase) to cast Rite of Undoing, targeting Palace Siege and any one of your creatures except Humble Defector. Palace Siege and your targeted creature return to their owners’ hands.
   4. Tap Humble Defector to activate its ability. You draw two cards, and Fitri gains control of Humble Defector.
   5. Spend to cast Friendly Fire on Humble Defector. Fitri reveals the only card in her hand — Palace Siege. Friendly Fire deals 5 damage to Humble Defector and Fitri, defeating her.
7. If Fitri chooses not to block any of your creatures:
   1. Your creatures deal a total of 7 damage to her. Fitri is now at 1 life.
   2. On your second main phase, tap two plains to add (both used as generic mana), two islands to add (one used as generic mana), and two mountains to add (one used as generic mana) to your mana pool.
   3. Spend and exile three cards from your graveyard (Frost Walker, Abzan Advantage, and Jeskai Runemark) to cast Rite of Undoing, targeting Palace Siege and any one of your creatures except Humble Defector. Palace Siege and your targeted creature return to their owners’ hands.
   4. Tap Humble Defector to activate its ability. You draw two cards, and Fitri gains control of Humble Defector.
   5. Spend to cast Friendly Fire on Humble Defector. Fitri reveals the only card in her hand — Palace Siege. Friendly Fire deals 5 damage to Humble Defector and Fitri, defeating her.