Are you confuseding how to play ROMs on Nexus 7, such as NES, SNES, GBC, GBA, N64, SEGA, ATARI, AMIGA, ZX, CAPCOM, or PSX? In the Google Play store, there is no classic games like Mario. With emulators, it's easy to play classic games on the tablet.
* SuperGNES Lite (SNES Emulator) Bubble Zap Games
The app offers support for Super Nintendo games with full console experience. Easily locate and play your favorite titles. It supports SMC, FIG, SFC, ZIP, and 7z formats and custom control mapping.
* NES.emu (Robert Broglia)
It emulates the classic NES/Famicom console on your tablet and allows you to pair a WiiMote as a controller. I often use the wii remote to play classic NES titles at home. But sometime screen freezes and then doesn't work yet on Jelly Bean.