The player is the Kid -- a rather diminutive, yet very ambitious character, whose goal in life is to gain the honorable title of "The Guy". To do so, he must kill the current holder of the title, but not before getting past numerous deadly platforming levels.
I Wanna Be The Guy is a platform game which is, in many aspects, a tribute to old-school '80s games - in terms of gameplay, graphics and difficulty.
Difficulty is perhaps the most prominent aspect of the game. IWBTG is (deliberately) an incredibly hard game, an endless chain of pixel-perfect dodging, jumping and manoeuvring; and of unexpected, surprise challenges, such as apparently harmless scenery objects suddenly becoming a menace. Some of the challenges may seem nearly impossible, and this isn't far from truth. Even the bosses (classic characters from '80s games) - while difficult - are still considered to be easier to beat than the platforming sections.
The controls are simple: the Kid can move left and right, shoot his pistol with Z, and jump with Shift. Jumping is, according to the author, "very controllable" - in other words, a little complicated: one can jump in mid-jump, and jumping height and distance are determined by how long the player presses Shift.
There are four difficulty levels - Medium, Hard, Very Hard and Impossible, but they differ only in the number of save points. On Impossible, there are practically no save points at all, so the whole game must be completed without a single death.