Ratty

 Ratty is a rat virus from the Mega Man Battle Network series that attacks by launching mini versions of itself (Rattons) that move in a straight line along the ground towards the player. These Rattons can turn once to seek its target. Rattys move around very fast, with stronger variants moving faster. When its HP is low enough, this virus opens its eyes widely and starts to move and attack much faster (the speed of the projectile remains the same).

Ratty
 Rattys are orange with an orange head. They also have a red light on top.

Ratty2
 Ratty2s are brown with a blue head. They also have a dark orange light on top.

Ratty3
 Ratty3s are gray with a gray head. They also have a blue light on top.

RattyΩ
 RattyΩs are dark gray/blue with a dark gray/blue head. They also have a geren light on top.