Love the difficulty. Took me a long time to beat it... finally read the comment: "Just keep running at the end."

Always get the movement speed bonus's (at least two) before the dinosaur miniboss. Always choose the power up that increases damage from the dinosaur for a life (it will be an empty heart if available).

Two winning builds I made with the original gun and character:

Fast Hands: Focus on reload/fire speed and how it combos with lightning. Get everything ricochet.  One level in damage.  Max out freeze for survival.

The Summoning: The flying daggers, ghost buddy, and lightning bug (2nd upgrade).  Only increase your damage as it helps your ghost buddy.