We knew to expect these cards from the Elspeth vs Tezzeret Duel decks, but we received a tip of what these cards do. We did not have photos, but it seems that these have been spoiled on MTGSalvation. See below and see what the new mechanic "Proliferate" does.

Contagion Clasp

Artifact

When Contagion Clasp enters the battlefield, put a -1/-1 counter on target creature.

: Proliferate. (You choose any number of permanents and/or players with counters on them, then give each of them another counter of a kind already there.)

Source: ManaNation.com

Kemba's Skyguard

Creature - Cat Knight

Flying

When Kemba's Skyguard enters the battlefield, gain 2 life.

2/2

Source: ManaNation.com