Standard WUB control deck.
A good hand consists of a balance of early removal, a variety of colours of mana, and a card to begin the draw fiesta. Reflector Mage is one of the best cards to have in your opening hand; the tempo swing it can provide is invaluable. In case of emergency, hit Descend upon the Sinful.
If in need of life, or pushing for damage, the Sorin and Narset +1 abilities combo nicely - Narset first, to see the card, then Sorin to drain life if it's got a decent CMC (the Silumgar dream).
Against Aggro:
Mulligan for Reflector Mage, Dead Weight and Grasp of Darkness. Ojutai's Command, especially in concert with Narset's -2, can be an invaluable asset with the extra life. Don't be afraid to use the removal abilities of the other 'walkers. Descend is best saved for when the opponent overcommits to the board or when you have the space to go on the offensive.
Against Control:
One of the most important cards is Shambling Vent as the 2/3 lifelink is especially potent. Don't extend the game too much as you are likely to draw your entire deck come turn ~20. Sorin and Ob Nixilis will win the game, especially with the latter's ultimate. Save Damnable Pact as a 10-damage nuke, as you'll almost certainly have the space to extract value from Painful Truths. Against creature finishers (eg Ormendahl, though he usually won't even get to swing), Silumgar can clinch the game on his own.
Against Midrange:
Use Descend Upon the Sinful to blow out their board, and follow it with your planeswalkers. Reflector Mage can generate huge tempo here, and Narset is an effective distraction that will likely generate advantage as well. Generally a favourable matchup.
Against Burn:
Similar to against aggro, Ojutai's Command and Narset are used to push you out of lethal range. Sorin is the other essential here. As a lot of spells in this deck drain your life, burn can be a difficult matchup unless you have good draws.
