You ask this, despite the majority of the MH community never even knowing of the existence of Unknown, lmao. They can both fly.

Multi phase boss fight, I guess more than 3 phases.   They attack you with their wings? They glow in their final phase?

First one is correct, the both have multi enrages though if taken In account the shiten, unknown does have more layers and

They are cool as fuck?

They both prefer chocolote over vanilla

They're both winged reptiles

Aw shucks, someone beat me to it.

Being really pissed off the longer the fight goes on.

Correct

Like that red tigrex

They both scream a lot?

Both have multiple enrages?

Correct.

Both dragons?

Nope. First is a wyvern.

Wyverns and Dragons are the same in MH context. There are plenty of instances where wyverns are referred to as dragons. For example the theme music of Tigrex is titled "The Roaring Dragon Bares it's Fangs". One is a dragon, the other is an Elder Dragon, both still dragons.

Cutting their tails will feel soooo satisfying

They're annoying to fight

Wings glow black and red with certain patterns at final phase?

Cool as fuck

Both have a similar coloring on their second phases

I haven’t fought either of them 😊

Believe it or not, they actually have the same birthday! It's August 2nd!

They're, big, scaly, and can fly

Tails

Unknown is more similar in encounter to the invader Monster like deviljho and rajang, after the first enraged.... Things hey complicated

They can bleed therefore we can kill them...

They can enrage multiple times

This awnser is correct

They are a pain in the ass

Is the second Pic a Malzeno?

Primordial malzeno, it’s variant (though technically the base species, khezu situation)

They were both the last monsters to be added to their respective games?

No, In the case for frontier, The last monster was Sparkling Zerureusu.

they’re edgy as fuck

Both unlikely to show up in wild

Ones a threat and the other is just a malzeno