Y'shtola, Night's Blessed

Two engines pointed in the same direction, stapled to the same 2/4 body. The end-step trigger is passive and symmetrical: it fires whenever any player has lost four or more life in a turn, which quietly turns a big combat step, a burn spell, or a life-heavy fetchland into a card. That half wants a table where life totals are already sliding, and it does not care whose spells did the sliding. The cast trigger runs actively, converting your own spellcasting into a drain: noncreature spells at three mana or more each ping every opponent for two and refund you two life. The two halves feed each other. Every trigger of the drain pushes a life total toward the four-loss threshold, so a spell-dense turn can trigger the drain and then hand you a card off the end step for free. Building around her still means choosing which axis to lean on, or threading both: a control shell casting expensive noncreature spells triggers the drain reliably but rarely clears the four-loss line by itself, while a more aggressive board leans on the passive draw and treats the drain as incidental reach. The Esper identity is what makes the second ability workable, giving her the counterspells, wraths, and removal that most naturally fill out a three-plus-mana noncreature curve. Vigilance is the small mercy that lets a defensive 2/4 keep pressure on without surrendering its guard.