8 Apr 2016
If you discard a card, the creature only gains haste until end of turn, but the +1/+1 counter and Vampire subtype remain indefinitely.
8 Apr 2016
If the entering creature leaves the battlefield before the triggered ability of Olivia, Mobilized for War resolves, you may still discard a card. The rest of the ability has no effect.
8 Apr 2016
You decide whether to discard a card as the triggered ability of Olivia, Mobilized for War resolves. If you do, the rest of the ability’s effects happen before any player may take actions.