Based on my experience, I didn't get solo. I did the test with druid 688, unfortunately the two dreadbeasts were not enough to kill Hellgorak. The "Drowning" damage of dreads was around 200 to 250 and Hell heals pretty much that. It's a difficult task, especially without the "mass "mas res", as it is necessary to keep healing dreadbeasts convinced of Hellgorak's attacks.
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A dreadbeast loses 258 hitpoints due to an attack by Hellgorak.
A dreadbeast loses 236 hitpoints due to an attack by Hellgorak.
You heal a dreadbeast for 258 hitpoints.
You heal a dreadbeast for 236 hitpoints.
Hellgorak loses 223 hitpoints due to an attack by a dreadbeast.
Hellgorak loses 244 hitpoints due to an attack by a dreadbeast.
Hellgorak healed itself for 453 hitpoints.