Clash Royale – How to Save a Replay Guide

The "lost cards on upgrade" is an illusion. (Well, poor interface design, to be percise.)
The upgrade animation shows draining of all cards, but the extra cards are actually saved. If you have enought cards, you can even upgrade a card multiple times in a row.

You should feel free to upgrade your cards without a worry. (Other than spending too much gold.)

I think that you can use the following strategies:

1. Attack the crossbow before it deploys. Stationary crossbows have a long deploying time, in which you can deploy a Mini P.E.K.K.A, Prince, a Musketeer, a Giant or any other fast/ranged/high-hitpoints unit to have enough time to get close and to destroy it.

2. Use a long-ranged spell. You can use a Rocket, Poison, Ligtning or a Goblin Barrel to cause a lot of damage to it from a big range. Fireballs may work too. You can also use Freeze to freeze the Crossbow for your troops to have more time to get close.

3. Let it destroy itself. (BUT ONLY it it's away enough from your towers) Buildings, including the Crossbows, slowly take damage over time and they destroy themselves at a certain point.