whenever a card is exiled mtg Elder Brain (CLB) #936 for as long as Assimilation Aegis remains attached to it Does Thran Vigil trigger when

1 Silent-Blade Oni

Along with that, as none of that relates to lifelink, you can pay two mana to give another target Creatue lifeline, and whenever you gain life, you can put a +1/+1 counter on a Creature or Enchantment you control

Since it's a Reserved List card from the 90s, copies of Unfulfilled Desires are pretty scarce, making it much more susceptible to hype-driven spikes like this one

And thats okay

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your opponent needs to not lose to the milling combo, but they also need to not lose to the giant 6/6 flying Demon, and it's much harder to make the latter a game-winning threat in a control deck that doesn't have other removal targets and doesn't apply pressure to life totals