One of the fiercest misnagdim…
Define fiercest. He was known to say some witty and snarky remarks on the chassidim and their minhagim, but not in the league or remotely close to the earlier Lithuanians who were bitter against chassidim. He never fought the chassidim and was actually close with them, interacted with them a lot and even admired some Rebbes (famously the Ateres Zvi of Ziditchov). He was greatly revered by all chassidim and it was the shtick for chassidisha lomdim in Lemberg to go to him to talk in learning and show him that chassidim do know to learn well. His talmid, nephew and successor - the שאול ומשיב was already extremely close with chassidim, revered their Rebbes and was famously the שר המסכים on many ספרי חסידות.
Go on
So that's how the story goes...
The מהר״ץ חיות became the rov in Zolkova and that position came with being the legal chief rabbi for the entire region, including Belz where the first Belzer rov Reb Shulam was the Rov. The Belzer rov, like all Chassidim in the area, was opposed to him as he was a borderline maskil and was close with maskilim and boycotted his legal cheif rabbi status. The מהר״ץ חיות initially tried to impose his authority on the Belzer rov and forced him to come and be tested by him to validate his rabbonis in Belz. That was the big march to Zolkova in the recent post. He also summonsed the Belzer rov to the gubernator in Lemberg to answer why he disobeys the מהר״ץ חיות legal authority. The Belzer rov came to the hearing in Lemberg and responded that he views the מהר״ץ חיות as one who doesn't follow tradition and Halacha properly and pointed to the טלית קטן of the מהר״ץ חיות saying that it isn't long enough l'halacha. (Belzer Rov was a big machmir..) The מהר״ץ חיות laughed and said that he can assure that the local famed rabbi, the ישועות יעקב, doesn't wear a longer talis than his. So the ישועות יעקב was called to get his talis measured... And, he showed up with an old and yellow looong talis! So the gubernator accepted the Belzer rov's tainos and exempted him from obeying to the מהר״ץ חיות. When they left, the מהר״ץ חיות asked the ישועות יעקב why in the world he's wearing that day such an old long talis so he answered that weirdly that morning he couldn't find his talis he had misplaced so he was forced to take out an old talis he had b'yerusha from his grandfather the Chacham Zvi to wear it... And the ישועות יעקב advised him against having disputes with the Belzer rov..
So that's a nice and famous chassidisha maisa, which you can decide to believe and you're not an apikores if you don't. (could be there are sources)