Warrior's Oath by paying its mana cost, causing you to take an extra turn after this one and to lose the game at the beginning of that turn's end step.
Activate
Magar by paying ({1} magic symbol) ({B} magic symbol) ({R} magic symbol) , noting
Warrior's Oath and putting it face down on the battlefield as a 3/3 creature.
During your next turn, deal combat damage to an opponent using the face down creature that has
Warrior's Oath noted.
The creature triggers, casting a copy of
Warrior's Oath without paying its mana cost. Resolve the copy, causing you to take an extra turn after this one and to lose the game at the beginning of that turn's end step.
Activate
Obeka by tapping it, causing you to end the turn. This will prevent the
Warrior's Oath trigger from causing you to lose the game.