Player you = game.getPlayer(source.getControllerId());
ManaCosts cost = new ManaCostsImpl("{X}");
if (you != null && you.chooseUse(Outcome.BoostCreature, "Do you want to to pay {X}?", game)) {
int costX = you.announceXMana(0, Integer.MAX_VALUE, "Announce the value for {X}", game, source);
cost.add(new GenericManaCost(costX));
if (cost.pay(source, game, source.getSourceId(), source.getControllerId(), false)) {
Permanent sourcePermanent = game.getPermanent(source.getSourceId());
if (sourcePermanent != null) {
return new AddCountersSourceEffect(CounterType.P1P1.createInstance(costX), true).apply(game, source);
}
}