This passive needs to be reconsidered or modified. Because of how battle order changes are handled by the logic, this “passive buff” ends up being more like a “passive debuff” on GT.
I see the following scenarios in PvP quite often:
Offense (in order): Zomm, Daeris, Shade, GT
Defense: N1, N2, N3, N4 (where N=normal speed)
What will happen is when Def N1 attacks, this hero is slowed by GT’s passive. Instead of Daeris, my first normal speed hero, going next, the def “second” normal hero - N2 - attacks. This is because N1’s speed is re-evaluated to slow (S1), and the order logic bumps everyone else up a position, making it S1, N1, N2, N3. Then, the new “first normal” speed hero attacks because in the new order, N1 hasn’t gone yet. This results in the def getting two attacks in a row purely out of RNG.
Now, another case...
Offense (in order): Shade, GT, Daeris, Zomm
Defense: Grog, N1, N2, N3
In this instance, Grog uses AoE and slows GT (and Grog is slowed as well). This will result in Grog, N1, and N2 all attacking before Daeris attacks - 3 attacks (plus pack tactics if all beasts). Grog is slowed, so he goes from N1 to S1, prompting N2 to N1 and so on. So the “new” N1 on the def attacks. Then, because GT was slowed and went from F1 to N1, it’s his turn... but he already attacked as a fast hero, so he gets skipped at normal speed. Then def “new” N2 (preciously N3 Before Grog was slowed) attacks. That’s a third attack in a row by the def. And finally, Daeris - my original N1 - gets to go.
Now, slow is a long-standing game mechanic. I accept it and am OK with Grog slowing GT and changing him to a normal speed hero. Ordering is a large part of the game mechanics and strategy, so let's not get distracted by that in my second case. I was just illustrating how this problem can easily be exacerbated.
But the GT slow on hit just adds more RNG to an already RNG filled environment (especially against beasts) that I don't think is necessary. A passive trait/buff should have benefit to the hero. This is mostly detriment from my experience, especially first round when the resulting impacts are the greatest.