Okay, first insight from building a simulator is about how stats buffs/debuffs act.
A debuff cannot bring attack, speed, or health stats down to zero. It can bring the shield stat down to zero. So if you have a monster with naturally one health and your opponent has a summoner that has a -1 health debuff your monster won't die before the battle begins, it will stay at one health.
After you hit "Rumble" the game applies the summoner's buffs/debuffs first, then the monster's buffs/debuffs. In the event of the above happening, the games does remember the -1 health though. So if you have a friendly monster with "Strengthen" you might think your monster with one natural health would go to two - that's not the case. Although the enemy summoner's debuff didn't change your health from one to zero, it does prevent your friendly monsters "Stregthen" from changing your health from one to two. The -1 hangs around in the background and cancels out the +1 if/when it comes up.
Happy battling!
