Upgrades can be made to your cards at the cost of 1500 coins per card once you've beaten the 500 score quest.
Purify is currently the only way to remove poison, and it costs 1 water quanta to cast. I suppose if you're using quantum pillars it might work, but you can probably find better ways to deal with poison. As Delreich said, Pulverizer is your best option, but it is a rare so you either have to win it or choose it as your prize in the 500 score quest.