Currently i am toying around with
Renegade Rallier in this slot. I have always like
Nissa, Vastwood Seer. When played at correct it generates so much value. It is only that i find it a bit awkward with
Nissa, Vital Force which has become an auto include in every build i play.
Rallier can also fix mana, although it is slightly more conditional. You need to crack a fetch, sac a creature or something must die in combat, etc. But it can potentially generate some other value like returning QPM or Sylvan Library. Next to
Recurring Nightmare or the Two Towers it can also get pretty nasty real quickly. I have always seen it as a lesser version of
Eternal Witness, but it has a different and interesting angle on itself. It is a pity that there aren't more targets for it in NicFit in general. Perhaps that a SFM version has most ways to exploit the card.