Elesh Norn, Grand Cenobite creates a dramatic shift in creature combat by giving your other creatures +2/+2 and opposing creatures -2/-2. Small opposing creatures can die immediately from having zero or less toughness, while your own tokens become substantial attackers. The effect is continuous, so creatures opponents play later also have to survive the toughness reduction.
Token decks make excellent use of the team boost. Three Soldiers from Elspeth, Sun's Champion become much more threatening, and a wide board can suddenly attack through creatures that previously blocked it profitably. White reanimator decks with black can use Reanimate or Animate Dead to put Elesh Norn onto the battlefield before they could normally pay seven mana.
The toughness reduction handles indestructible creatures if their toughness becomes zero or less, because that is not destruction. It also makes damage-based removal and combat trades more favorable against larger creatures that survive. Creatures with death triggers still trigger when they die, so consider opposing aristocrats engines before assuming the board change is entirely one-sided in its consequences.
Elesh Norn does not give herself the +2/+2 bonus, but vigilance lets her attack while remaining available to block. Her strongest role is often stabilizing the board immediately and turning an existing army into a finishing force. Protecting her matters because removing her restores opposing creatures' normal stats and takes the bonus away from your other creatures.
