I can clearly remember, that she never had this interaction. I can't find Toast's/Hysteria's video, where this was tested, but Sylvanas Windrunner could never steal the Nether Portal, since it didn't count as a minion. Enigmatic Portal was a different story - visually it looked like a dormant creature, but in reality it classified as a minion. This is why people managed to turn into the Cow King in that tavern brawl.
I've mentioned, that there are other minions, that interact with the number of bodies on either side of the board and those can be Mind Control Tech, Knife Juggler etc. Imagine, that I have a dormant The Darkness on the floor and 3 other minions, my opponent plays MCT, but can't steal anything, because the game observes my board as if it consists of only 3 threats. Same case with Sylvanas - the Portal is an enchantment.
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aha yeah. now you said it. cow king. i guess i mistook it for nether portal. anyways thanks.