Use this card in a Final Countdown Deck, because Final Countdown's effect would reduce your Life Points by 2000, fulfilling the activation requirements. Then, you can use the effect of Frozen Soul to skip your opponent's next Battle Phase and stall for time.
You can also use this card in an Inferno Tempest Deck, because Inferno Tempest requires you to take at least 3000 Life Points in Battle Damage in order to activate.
Your opponent needs to attempt to enter their Battle Phase in order for the skip to take effect. If they proceed straight from Main Phase 1 to End Phase, the skipping effect is retained over subsequent turns until they decide to enter it. Many players assume Frozen Soul's effect lasts for the turn and immediately end their turn, and take the full brunt of Frozen Soul's effect several turns later.
Remember to let know your opponent how this card's effect works. Otherwise, it is considered cheating for not letting your opponent know how the effect work and may get you in trouble in tournaments. After letting your opponent know how this card's effect works, then it becomes their responsibility to apply this card's effect properly.
This could still be somehow useful. If somehow you can activate this card during your turn or after your opponent's Battle Phase, then after setting up your strategy during your turn and their own strategy during your opponent's turn again might divert your opponent's attention of having them applying this card's effect themselves.
Remember that you can activate this card during your own turn and still gain its effect. So, if your opponent uses an effect like Dust Tornado to eliminate this card during your turn, you can chain it and keep them from attacking on their turn. This also lets you free up space if you need to use a more important card, something you can't do with cards like Threatening Roar.