-Deal at least 10 Damage + 10pp Aisha
-Board + Catacomb
-keep the enemy from having board control
-prevent your death at turn 10 by Sythetic Beast
Works for me at least (Master Rank)!
My Mid-Shadow deck:
If that doesn't work... there is still the option of using another deck.
The trick to winning against portal is to let them counter themselves. Don't play their game. Of course you're gonna lose if you keep trying to control the board against Acceleratium-boosted artifacts. One card that demolishes their board is Odile, since most of their artifacts have low health and high attack. Prioritize getting chip damage in then finish once they run out of gas.
It also depends on what you play. All 3 meta decks in rotation can easily defeat portal in their own playstyle. Shadow can create a sticky board that leads up to Eachtar or Aisha lethal, Rune can slowly burn them down then blow them out using Levi at turn 6, while Dragon can just ignore their minions, ramp into Bahamut or Israfil and at that point, there's nothing much Portal can do.