yeah, charizard gets hurt in the air, but not nearly to ivysaur's extent, thanks to faster horizontal air movement than meta, more weight, rock smash (mainly because its faster than ivy's fair), and better recovery. i cannot count how many times fly SA has saved me from a dair gimp. the thing is that, like ivy, dair is zard's only option underneath. uair ***** zard at low percents. don't let it happen.
like ivysaur, zard wants to keep mk grounded. flamethrower stops everything mk has that isn't tornado...but don't get predictable with it, and make sure to use it when mk is dashing into range or short hopping, or is vulnerable somehow. if mk sees ft coming, you'll just get tornado'd. btw, i prefer using rock smash to break the tornado, although ftilt and bair are also options. rs sometimes won't work, but just work on the spacing and timing for it. idk if zard can grab mk out of tornado due to the way zard lunges to grab, thus extending its hitbox.
don't get down smashed and zard should live to nice percents.
zard also kills mk well. dtilt/utilt/ftilt/usmash/rock smash/throws anyone? ivy does not have nearly that many options. fair is ivy's best, safest kill move that isn't a throw, and an auto-canceled fair is PUNISHABLE by mk thanks to his dash speed and dash grab. and as everyone knows, all of ivy's other kill moves are pretty punishable, even against characters that aren't mk.
however, uthrow kills consistently at like 150%. definitely a life saver from about 120% on to switch or kill.
seriously...don't use ivysaur in this matchup. its worse than rob.