At first i thot you meant instead of Sulli, but now after posting my puck of Krystal in Running Man episode(go check it out), i realuse you meant Sulli AND Krystal were supposed to be on this episode together, idk they usually wouldnt put 2 similar idols from 1 group in the same episode of Running Man, either Sulli and Luna or Krystal and Luna seem more provavle, not Sulli and Krys together.
The variety shows hv their formula and its all or they just pick 1 pretty (according to their prejudices) member of a group, n another non-visual if they pick 2 in a group. Or they get all (except the busy member) 8 out of 9 in SNSD so they avoid choosing who not to pick, at least from wat i rmbr of watching first 160 episodes and l8r 200 episodes of this show. I might be wrong n misremembered (tats 350 freaking eps, cant rmbr every single thing, LOL) Victoria and Amber, separately, also appeared in a gg centred ep but not with fellow members iirc.