This is really too much... And I'm hearing about this bug for the first time, probably like most users of this forum. So, in my opinion, it's not prohibited.
Hmm... This bug has been known for a long time. I think they should fix it in 3.1.
I just ran that battle again and recorded a replay of Krag in the Mask... Well... 100 Dragons in 5 hits - that's harsh... But in the replay, Krag's level is shown as 8, although it was displayed as 70 in the battle...
So, in the actual game, you can bribe him after a couple of hits, which are comparable to the Warlock's Earth Shock...
Горящие реки сходили с ума, пытаясь остаться водой,
Земля пропустила коварный удар, раскрывшись на шаге вперёд,
Взлетел разъярённым драконом Огонь и понял, что тоже умрёт...