An instinct to bask in the sun and rest all day

A compulsion to toy with prey, sometimes maliciously

An urge to eat as many humans as possible, for enjoyment rather than survival

A need to pose, move dramatically, and be close to/touch people to whom he is speaking
         At phase 3 becomes an almost thoughtless compulsion to invade personal space.

Increased tendency to hold a grudge, especially against people who have been given help and not repaid in kind to his satisfaction.
         This resentment will become more and more violent the longer the grudge is held.

Increased defensiveness. Anything perceived as a failure will be covered up and deflected from.
         Goes hand in hand with a desperate need to be perceived as good and without fault.

Longer tail
         38 feet; 10 grown at level 1 infection, 3 grown at level 2 infection.
         Rattle also increases in length from 6 beads to 12, turns bright red.

Sharper claws

A single spike growing out of the center of his back

A vastly larger mouth that hinges beneath his ribs
         Pictured below. He can speak without opening the entire thing, thankfully.

Blue, acidic blood that can melt metal.

The ability to summon warm rain in a close radius.
         Useful for decreasing visibility. Can cause localized flooding.

Art refs:
         x by me