With no creatures on the battlefield, your best option would be to look for either a direct damage spell or some creatures with haste. Thundering Giant won’t cut it, since casting him will use up most of your available mana. But your graveyard does offer up another possibility: Altac Bloodseeker.

1. Tap six mountains to add (five used as generic mana) and three plains to add to your mana pool.
2. Spend to cast Return to the Ranks, targeting four creatures in your graveyard: Altac Bloodseeker, Torch Fiend, Selfless Cathar, and Kinsbaile Skirmisher.
3. Kinsbaile Skirmisher’s ability triggers. Choose to give the Altac Bloodseeker +1/+1 until end of turn. The Bloodseeker is now a 3/2 creature.
4. Spend to activate Torch Fiend’s ability, sacrificing it to destroy Voytek’s Juggernaut.
5. Altac Bloodseeker’s ability triggers, giving itself +2/+0 and gaining first strike and haste until end of turn. The Bloodseeker is now a 5/2 creature.
6. Spend to activate Selfless Cathar’s ability, sacrificing it to give all creatures you control +1/+1 until end of turn. The Bloodseeker is now a 6/3 creature.
7. Declare the start of your combat phase, assigning your Altac Bloodseeker as an attacker. Voytek has no creatures that can block it, so the Bloodseeker deals 6 damage to him, defeating him.