How do you unlock the secret weapon for thing thing 2?

Answer 1

To start, there is not a "secret" weapon but a bunch of weapons which can be unlocked.

One to each level that can be unlocked by meeting a certain corpse quota (go for the sweet 80-100, and the game will count it and label you a sociopath or death god).

I.E. you can kill about 15-20 people, using the Desert Eagle, on level 3 (the falling level) to earn an MP-5

Also there's a shotgun (Striker 12) to be earned in Thing Thing 2 Survival Mode by killing 200 to 400 people. I recommend the MP-5 and Glock for this achievement.

Now if by "secret weapon" you mean the boss Zeus's assault rifle, yes, that needs to be found.

There are two checkboxes near his level: one for that Glock (earned by killing 100 people before Zeus), and the other for that huge rifle he holds. How you get it is by some means within the boss fight. I don't know what to do.

Hell no!

the two boxes at the bottom of the boss level are for the glock and a desert eagle improvement

it goes:

Level 1-MP7

Level 2-Handgun upgrade

Level 3-Mac-10

Level 4-Desert Eagle 1

Level 5-Shotgun

Level 6-MP5

Boss- Glock + Desert Eagle 2 (also you get a Zeus suit and mask in the character create)