Like most abilities on creature cards, Glimpse, the Unthinkable's abilities only apply while it's on the battlefield
My turn 5: use lotus petal, 8/8 Warden (Opponent at X-8 life) Opponent turn 6: 8/8 warden (Opponent at X life) My turn 6: 13/13 warden (Opponent at X-13 life) Opponent turn 7: 13/13 warden (Opponent at X life) My turn 7: 18/18 warden (Opponent at X-18 life) Opponent turn 8: 18/18 warden, and activate elixir (Opponent at X+5 life) Alright, cool, so at the end of my opponents 5, if I save my Lotus Petal, my opponent needs to be at 19 life or higher
Turns 10+: Close out Board presence and the card advantage you built dictate the close
It can even provide a burst of direct damage, much like Cut // RibbonsCut // Ribbons
Both she and the alternate commander, Celes, Rune Knight focus on milling cards to the graveyard and then reanimating creatures to fill your battlefield