Choose your evil life form. Mutate. Spread. Kill.
Upgrade your critter with symptoms like vomiting, sweating, delirium and open sores. Yummy!
Become God like Parasite/Bacteria/Virus.
To get under the "radar" try to be as invisible as possible. That means don't buy any symptoms in the begining, spread to all countries and then mutate, to create leathal critter to wipe out the entire planet!