As far as stratagy the best advice I can give is use your pow's wisely and don't forget that you can stand on the pow to avoid enemies, but beware of the fireballs!
On the bonus stages start running to the left get the coin run through the screen get the other coin and keep running past the pow, then quickly jump to the next level and repeat this until you get the last coin. Keeping Mario running is the key. You get 19 seconds in the first bonus round but only 15 seconds after that so be quick.
CODE/EFFECT . . .
SXTIEG/Infinite lives
AAISPL/Start with 1 life
IAISPL/Start with 6 lives
AAISPU/Start with 9 lives
PENGSAAA/Faster Mario(tm) & Luigi(tm)
ZENGSAAA/Mega fast Mario & Luigi
VYSYAUKY + VYSYPUKY/Mega-jumping Mario & Luigi
EZEKEPKZ + ZAEKOPNG/Faster baddies
EZEKEPKZ + LAEKOPNG/Mega fast baddies
AEUIUGAG/Coins kill you! Try this code without telling player two!