I can see why the cops ride these in Waterdeep, that's a fast bird!

The griffon. One of the most iconic fantastical beings. 

Lost Keen Sight, just like everything else. 

Attacks were changed from Beak and Claws to generic Rend. Average damage is decreased from 8 piercing and 11 slashing to 16 slashing. Even max damage is lowered from 28 to 24. However, the claws on the new Griffon now automatically grapple if the target is medium or smaller, which player characters are. 

Not many changes going for the Griffon. Still, it is what it is.

Fusion time! The best fusion option I got for these guys would be to simply revert the Rend's damage die from 1d8+4 to the 2d6+4 slashing from the 5e griffon. 

This thing is insanely dangerous. It's one of those monsters that fights way above its CR rating suggests if used with the correct tactics.

If DMs play it like a proper bird of prey, it will only ever fight one PC at a time: Fly in, attack someone, auto-grapple them, gain altitude away from the rest of the party. Maximum carry weight for a large, 18 Str creature is 1,080 lbs. Even half of that is way more than any PC weighs.

"Dragging" a grappled creature reduces movement speed by half, so 80 ft fly becomes 40 ft which is still way faster than most PCs can keep up with even on land. 40 ft. of a shallow Climb (30 deg) is 35 horizontal ft. and 20 ft. of altitude. A steep climb (60 deg) is 20 ft. horizontal and 35 ft. of altitude.Which means, best case scenario, a grappled creature takes 20, 30 or 40 ft of fall damage even if it frees itself on its turn. Double that if the Griffon uses its turn to dash instead of attack. 

A hunting bird of prey will try to ambush the party. Give it a Stealth check against the party's passive perception to come outside of their sight lines. Maybe flying out of the sun.

When it begins its attack, it'll go for the most vunerable-looking member of the "herd" in the first place: No armor, and smallest first. Maybe give it a perception check to size up the group, so that it has a chance to notice if the "smallest" creature is actually a halfling barbarian and change targets. Otherwise most of the time the most vulnerable-looking target will be a caster with "soft" skin and low str.

Then after its first attack, the fight will immediately become a rescue more than a slugfest. Its top priority will be to carry its prey off to a safe place to eat it. Maybe it's nest. The only reasons it would have to turn and fight if its first attack fails would be if the group had been ineffectual in fighting it off, if it was starving and desperate, or if it had a rider directing it.

So, in summary: Sneak, ambush, grab, retreat. If it's a hunting, wild Griffon keep retreating with the prize. If it's a war Griffon drop your target for that extra fall damage at the end of the turn.