Put down a really weak monster then asap use aflatoxin on it. It will turn into a malignant cell and multiply every turn.
If you have a spell that heals you for every monster you have on your field like Empathic Bond then play it.
If the opponent uses a shield use defilagration to destroy it. The only problem is that they can have something that destroys all of the cells and thats not good so if you can, get a blessing in there too and use it on a malignant cell.
Throw in some other monsters like a dragon or abomination just in case you dont have a defilagration in your hand when they use a shield.
==EDIT== Another good idea is to have a bone wall or two, so if the use thunderstorm of rain of fire, you'll have a nice shield to hide under before you get back at them - Hobnob5000