With Trostani on board, a single token can quickly grow into an army, and if that token is big enough, our army can quickly close out the game
Run her with Eldrazi and she can ingest, discard, and destroy, creating a crazy control deck
She gains Time counters for all the other suspended or vanishing cards you have lying around, becoming more powerful as she does so
This creature can't be the target of spells that can target only Walls or of abilities that can target only Walls
Regarding steel, there are some cards that can help with this overarching damaged character control strategy, like Tug-of-War, which gives the player a choice of dealing damage to all opposing characters with the Evasive ability or without, or Yzma, who can deal 1 damage to a character if any of the players characters banish another character through a challenge