Pvp is turning lame as fuck. Getting crushed. Put up against higher ranks.... Overpowered with no reason for it.... Losing and I don't understand why.
Gotta watch when the enemy's health is low. He has 3 stages. Make sure not to drop guys when you're about to knock him out of a stage. He has a large explosion that'll take out most of your guys.
Avoid dropping guys 1 at a time. Play defensively. The best defense is one that will eliminate the enemy and survive to make a counterattack.
Know what counters what. If he throws down an assassin, consider countering with something like pigeons or a flying unit. That way you can take out the ground guy, without him being able to even attack your guy.
Know your deck. Have an idea of what's on your field and what's in your hand. That way you can predict what cards you will draw next. This brings up cycling. Using a lower cost card, even though it may not be the most effective, because you know it will allow you to draw a certain card that you need.
TL;DR - Know when to drop. The best offense is a surviving defense. Counter properly. Know your deck (cycling cards).