Animator2D is a simple animation library that allows you to string together (sequence) different animation behaviours. Sequences can be re-used for each movable object ('mob' from now on) in your scene. Mob's will always have a position (Vector2) and a heading vector (Vector2). The heading vector is a displacement so it tells you both where to and how fast.
Animator2D is designed specifically to animate mobs in scrolling shooters. Because sequences are reusable, mobs that follow each other are as easy as waiting a predefined period between assigning sequences.
Sequences are implemented per mob allowing special cases per mob, such as a position offset. This allows for other group formation effects.