If your cube is going to have a rare cycle of Legendaries with both Phage and the Nalaars, maybe these suggestions could help fill out that cycle:
White:
- Since you are going with
Phage, she's most normally paired with
Akroma, Angel of Wrath, but I'd suggest trying a different angel on for size.
Avacyn, Angel of Hope is the same cost and arguably fends off Phage just as well (if not better), while her smaller version,
Avacyn, Guardian Angel, comes down quicker and offers more choices while also being a good stop to Phage. On the non-angel front,
Cho-Manno, Revolutionary is also a good Phage stopper, as is
Commander Eesha.
Blue:
- Everyone (me) is always a fan of
Arcanis, but we're trying to shy away from just reprinting all the pit fighters. If you wanted to see if a Morph/Megamorph theme could fit into your Vorthos Cube, I'd suggest
Ixidor, Reality Sculptor. Still that leaves us deep in a weird time for Magic's Storyline. It doesn't get more flavorful in Blue than
Teferi, Mage of Zhalfir, and there
are a lot of spells he's quoted on that would make good Cube filler, especially if you are going for flavor.
Sakashima the Impostor may also be fun while filling your obligatory
Clone slot.
Green:
- I was going to suggest
Eladamri, Lord of Leaves if you were going to have an elf component, but his design is old and leads to poor game play.
Melira, Sylvok Outcast doesn't work unless you really go all in on -1/-1 and poison counters or add in
Kitchen Finks-like cards for real silliness.
Mirri, Cat Warrior, as a character, is amazing, but her card is really underwhelming.
Thelon of Havenwood would be nice if there was going to be a tribe for him to support.
Thrun, the Last Troll is pretty flavorful in his own way.
Yeva, Nature's Herald is an interesting counterpoint to Teferi if you use him. Green just doesn't really have that many compelling legendaries that aren't really niche.