First, don't be intimidated. That's what they want. Second, try to be smart about it and prepare carefully. For example, even under this awful law it's not illegal to annoy World Youth Day participants (although you can't obstruct the event) - it's only illegal to not comply with a direction to stop. With the right idea, it may be possible to make a good statement, or even just a good joke, before anyone asks you to stop.
Remember, you're not committing an offence if you have a reasonable excuse - in the end, a court will decide what's reasonable. But if you conduct yourself in a calm and sensible way and try to stick to the rules, you'll give yourself a better chance of getting away with it.
Finally, film everything for as long as you possibly can (mobile phones are great for this) and try to make sure you keep the footage. Even just seeing the ridiculous situations this law creates, and potentially the heavy-handed way it gets enforced, might help turn the tide against bad governments passing bad laws.
I'm very tempted to buy a Pope Day T-shirt from Remo - "Sponser a lion for WYD - ask me how!" is awesome.