I think I've beaten every Mario game ever bro

Counting only games with Mario in the title that I have completed to the credits:

Mario Tennis (N64, GBC, GC)
Mario Golf (N64, GC)
Paper Mario,TTYD
Kart (Super Circuit, 64, GC, DS, Wii, 7)
Mario Party 1,2,3,5
1,2,3,World,World 2,64,Sunshine,Galaxy,Galaxy 2,3D Land
NSMB (DS, Wii)

29?

Mario RPG
Paper Mario and sequel
Idk how many Mario Parties
Mario 64
Super Mario world
luigis mansion?
Sunshine

Just three:
Super mario galay
super mario 3d land
nsmbu

SMB, SMB2, SMB3, SMW, NSMB, NSMBW.
Yoshi's Island 1 and 2.
SM64, SMS, SMG1 and 2.
MP5 and 8.
SML, SML2 and SM3DL.
Luigi's Mansion (if it counts) and Wario Land.
Mario vs Donkey Kong (GBA)
=
20

More than 10 I reckon.

i've played many of them (from NES/ game boy to Wii/DS) but not beaten any of them

A lot. Mario is just in too many different games across too many different platforms to even attempt to play or beat them all. I can't even remember all of the Mario games I've played. I can say that I skipped every Mario Golf, all of the Mario Parties except DS, Wii, and one of the N64 titles, all of the Paper Mario games except the first, Partners in Time on the DS (but I will order this, soon!).

Anyhoo, all of the Mario Karts, all of the 2D platformers, all of the 3D titles, Mario RPG, and some other spinoffs. I don't have a billion dollars to spend on Mario games.

Do crossover games like Somari count? http://en.wikipedia.org/wiki/Somari

30+ and enjoyed the vast majority of them.

Super Mario World still gets my vote for greatest Mario platformer of all time.

Onyl Yoshis Story.

Yes, I suck at games.