As her Revival Trance deck puts it, fill your graveyard and revive your fallen heroes. Put simply, Terra lets you return a creature from the graveyard to the battlefield at the price of 2 mana whenever she damages a player
And as someone who has cast Boom // Bust on a Darksteel Citadel plenty of times, there are a lot of options to choose from
Wizards has been good about not throwing any huge curveballs here since the 30% hurdle in Commander Legends, and it makes these calculations a lot easier
The card is very inconsistent: sometimes Mangara will draw you a ton of cards, sometimes it won't draw you a single card, it's all up to your opponents
Of the black legendaries in the set, I really love Shadowheart, Dark Justiciar, who is an excellent Commander and card in the 99 of decks with big creatures