For searchability sake, I wanted to link to a rules discussion that resulted from a tense XCAPS19 game, and @sharpobject if you are able to chime in with official confirmation that’d be swell 
Situation is that one player (@Marto) controls a Blooming Ancient during the opponent (@bansa)'s turn, and the opponent plays Terras Q, the Shackled, granting the player 4 warlock tokens. The general consensus reached was that the Blooming Ancient would receive 4 +1/1 runes, one for each warlock, as they arrived under his control with the arrival of Terras Q.
See here for full context, pretty spectacular to see a TerrasQ + Discord combo get immediately countered by raw combat damage like that!
It would follow that the same would apply for Final Showdown (or any other card I’m forgetting?) and the two Hunter tokens given an opponent in control of a BA.