If I play the Harrowing and target darius Trifarian from my trash will he enter ready?

Clarify that this interaction won't work from Set 6

Yes — as long as The Harrowing is your first card played this turn. The Harrowing resolving and playing Darius from your trash counts as playing a card (FAQ #9614). So the sequence is: The Harrowing = card 1, Darius entering = card 2. Since Darius is already on the board when the "second card" condition is checked (Rule 419.4.a; FAQ #1119), his ability fires — he gains +2 Might and readies himself, even though he entered exhausted like any unit played by an effect. If you'd already played a card earlier that turn, The Harrowing would be your second card and Darius your third — past the trigger window — so he'd stay exhausted (FAQ #9420). However keep in mind that when Legacy, which is Set 6 comes around the meaning of "when you play ... [card/spell]" will change to checking finalization instead of resolution, so this interaction won't work from then on. https://playriftbound.com/en-us/news/announcements/products-and-sets-into-2027/