Older players will recall the classic Channel/Fireball combo, and this Standard-legal combo is basically the same idea, albeit a little riskier.
Here’s how it works:
With Immolating Souleater in play, cast Assault Strobe and attack with the Immolating Souleater. If he gets through, pay as much red mana as you can afford, and use your life total to pump him the rest of the way to victory. Since he has doublestrike, and starts with a power of 1, you are going to remain ahead of the game (especially if you can afford to pay some of it with red mana instead of life).
Even without red mana available to pump it, an Assault Strobe’d Immolating Souleater with 18 life paid into it will deal 20 damage (18 life buys it +9/+9 for a total of 10/10, dealing its damage twice for a total of 20 damage to your opponent, as long as it was not blocked and no damage was prevented).
This can be accomplished at a very early stage of the match (turn 3 or sooner). Just beware an opponent responding with their own instant-speed direct damage at your life total!