def action = {
    final MagicGame game, final MagicEvent event ->
    event.processTargetPermanent(game,new MagicPermanentAction() {
        public void doAction(final MagicPermanent permanent) {
            game.doAction(new MagicSacrificeAction(permanent));
            final int toughness = permanent.getToughness();
            game.doAction(new MagicChangeLifeAction(event.getRefPlayer(),toughness));
        }
    });
} as MagicEventAction

[
    new MagicSpellCardEvent() {
        @Override
        public MagicEvent getEvent(final MagicCardOnStack cardOnStack,final MagicPayedCost payedCost) {
            return new MagicEvent(
                cardOnStack,
                MagicTargetChoice.TARGET_OPPONENT,
                this,
                "Target opponent\$ sacrifices a creature. " + 
                "PN gains life equal to that creature's toughness."
            );
        }
        @Override
        public void executeEvent(final MagicGame game, final MagicEvent event) {
            event.processTargetPlayer(game,new MagicPlayerAction() {
                public void doAction(final MagicPlayer opponent) {
                    game.addEvent(new MagicEvent(
                        event.getSource(),
                        opponent,
                        MagicTargetChoice.SACRIFICE_CREATURE,
                        MagicSacrificeTargetPicker.create(),
                        event.getPlayer(),
                        action,
                        "Choose a creature to sacrifice\$."
                    ));
                }
            });
        }
    }
]