Interesting to note that, so far, Zayne has one unique type (Dispel) and Rafayel has two unique types (Pull and Debuff). This is most likely from an attempt at balance when it was still just the OG3.

Rafayel is missing Control, Defend, DMG, and Dispel; Sylus is missing Support, Defend, Buff, Sustained, Heal, Dispel, Pull, and Debuff; Caleb is missing Control, Single-target, Support, Buff, DMG, Heal, Dispel, Pull, Debuff, and DMG.

For the companion types, we can probably predict according to what types the boys are missing currently. Including the non-myth companions and from the types we have so far, Xavier is missing DMG, Sustained, Heal, Dispel, Pull, and Debuff; Zayne is missing Buff, Pull, Debuff, and DMG;

I was trying to see if I could predict stat buffs but any patterns/trends I noticed were inconclusive. The only one we know for sure by process of elimination is Caleb's next myth which will most likely be HP.

Sylus
Relentless Conqueror = pink/pearl
Abysm Soverign = green/emerald
Silverwing Fiend = blue/sapphire
Next myth = likely purple/violet

Caleb
Farspace Colonel = red/ruby
Ulimate Weapon X-02 = purple/violet
Next myth = likely green/emerald
Next myth after that = likely blue/sapphire

Rafayel
Abysswalker = purple/violet
God of the Tides = pink/pearl
Lemurian Sea God = yellow/topaz
Next myth = likely red/ruby
Next myth after that = likely green/emerald

Zayne
Foreseer = blue/sapphire
Master of Fate = red/ruby
God of Annihilation = pink/pearl
Next myth = likely yellow/topaz
Next myth after that = likely purple/violet