The coming of the Demon Goatbeast was signified by a torrential, flammable, blood-red rain accompanied by thunderbolts. It seemed to suffer no damage from any of Voltron's attacks (even that of the Blazing Sword) until he wielded the Electro-Force Cross against it.
It may be argued that, without the Cross, Voltron would not be able to defeat such a foe.
Clearly there is a connection between the Hellstorm and the summoning of Hell's servant...or sultan.
The Demon Goatbeast...
It's on like Voltron....
...And not a split instant too soon!
The Beast is even stronger than Voltron....
...so Voltron fires his flamethrowers....
...Which mean nothing to a monster summoned from Hell!
Voltron braces for Round 2.
The Demon can either fly or jump extremely high...
...and being ready...
...doesn't make Voltron any stronger!
Narrowly avoiding the severance of his left arm, Voltron prepares to lay down the final blow.
Direct hit from the Blazing Sword! Now blow up!
Any time now....
OK, maybe it will be delayed, like in Fist of the North Star!
...You're not going to blow up, are you?
Voltron follows up with the Lion Torch.
Ummm....I haven't stopped being immune to fire in the last 15 seconds!
Again: immune to fire...and that sword Voltron is about to bring down...again!
The Demon Gloatbeast.
Laser eye surgery.
At last they understand.
Is this what was seen by Constantine?
The Cross descends on the terrified Demon...
...and with a blinding flash...
...it becomes the Mark on the Beast!
It burns! It burns!
I'll just stick my toe in to make sure it's safe....
No! This cannot be! Voltron's attack causes me to feel PAIN!
The Demon's sword passes harmlessly before Voltron's blazing one.