Nah, bair is only useful in this matchup as a means to keep zard honest. Throwing it out constantly is counterproductive after you've set up the initial threat. Dtilt, fair, and leaf are much more applicable (see... 2:04, ) especially at low %.
In essence, your main problems is that you're not really getting enough off your hits, you're throwing away neutral or you're committing to something within a punishable range, and you're not abusing your good situations. You're also kind of slow sometimes(?) and you tend to retreat after getting hits even when the exchange favors you taking space.
Getting more out of your hits:
--FOLLOW UP ON FAIR WHEN YOU HIT HIM (2:33, 4:02)
--Nair instead of bair in a combo situation
--Very often you settle for a grab when you could easily set up an usmash or grounded dair (which leads into everything)
Stop throwing away neutral:
--Very often, you put out moves at unsafe distances (leaf especially) or fall into a rhythm (bair especially)... see your last stock on GHZ for particularly egregious examples of this
--Abuse dtilt's complete ground dominance to force Zard to jump
--Please stop letting him run up->PS leaf->anything
Abuse good situations:
--If he's in the air, you have the advantage, especially if you forced him to jump and he's facing you (no threat of instant nair)
--If he's on a platform above you, you have the advantage, and you should be pressuring him VERY HARD with uair->seed bomb, vine whip, nair, and WL grab. The tendency vs most Ivysaurs is to shield once we get them pinned on a platform, then act OoS as soon as we do anything (this is why uair->seed bomb is amazing).
--If he's on the ledge, especially if he already used his glide, he basically has no options. Wait him out, use synthesis if necessary to remind him that he needs to do something or you win the game, and hit him for whatever he does (nair if you can get it, bair otherwise). Many PM players
really really like to press X or Y and ledgejump. Turns out, everyone really really enjoys ledgejumping directly into vine whip sweetspots.
Other stuff...
--Don't roll out of dthrow tech. Mixing it up between tech in place->jab/ftilt/dtilt/dsmash/roll/spotdodge and missed tech->get up attack/neutral get up->jab is VERY hard for zard to cover, especially compared to our mediocre techroll.
--Another grab thing, you should probably be preemptively DIing behind Zard to cover the bthrow mixup. He never used fthrow so it's not REALLY a mixup, since worst case he will use dthrow or uthrow and you have plenty of time to react to those. Bthrow sets up into fair/uair/side b shenanigans if you get caught with bad DI.
--Stop burning your midair jump so much. Look at 10:33 or 17:45 and I'll give you a cookie if you can come up with one good reason why you should throw away your double jump way out over there. It's very likely you would've died for it, had he been patient enough to just sit on the ledge.
--Practice acting immediately after other things. L cancel SH bair into DD, FH fair waveland, nair->jab...
tl;dr nair more
Sorry if this was really confusing, I'm juggling lots of stuff today and in a bit of a rush. Got to calm down for a few minutes and watch some solid Ivysaur play so I appreciate that