Use Ragnarok, wait till the first dragon is about to fire.
Use the Holy Grail. Now all dragon blasts do nothing.
I hope you are still shooting at them while waiting for the day to end. They give good exp.
It matters little to me anyway, Auto bowguns with max Bowmaster and damage mods means Clearing rows of them quickly.
1 Pick Virus
2 Start in Canada, Greenland, New Zealand, or Cuba (if not, restart)
3 Sell starting symptoms (if any), other than sneezing. If you don’t have sneezing, buy it
4 Buy 1-1-1-0 Resistances
5 Once your disease spreads to a few thousand people, sell sneezing to get rid of visibility
6 Wait until all countries are infected. If Madagascar closes or this is after day 30, restart
7 Pump 4 Drug Resistance and buy sneezing, coughing, vomiting
8 After a few days, unlock tier 2-3 keeping whatever symptoms it gives you
9 Buy fever, fatigue, diarrhea, pulmonary edema, hypersensitivity, hemorrhaging
10 Wait until everyone dies
A bit of experimenting showed that China and India are bad, since population explodes too early. Russia and Africa because your initial spread takes too long. Europe and the Asian continent because you tend to infect too fast via borders, and make South America and the islands panic before you get them. South America because the place is relatively isolated.
I used heisierjeg's method, except with one difference, I sold sneezing as soon as I had about 5000 infected people in my starting country. They only start closing stuff when your starting country is between 1/4-1/2 infected, or when a certain threshold of total infected in the world is reached. So you'd want an initial 5000+, which is enough to spread to another country within a few days and is also the bit where your fluctuating infected becomes exponential growth.
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 "Pandemic 2"){kind=icon}