morph
u w - flicker: yorion, brago
-bounce to hand: niambi(lets you recast morph or kicker)
w g - sidar
u r - ludevic (Morph/goodstuff)
w b - kambal (punish non creature decks), ravos (return creature from gy to hand)
g u - ezuri (morph make xp), volo (create 2/2 token army)
g u w - roon - flicker morphs
b r g - sek'kuar, tokens on death of morphs
b g u - kadena, slinking sorcerer(best morph commander?) card draw and free morph
u r g - animar (morph voltron, and reduction)
r - subira (draw cards from your morph creatures)
u -jalira master polymorphist (turn morph into something bigger?) ixidor (morph lord and turn morphs face down again!)
g - nylea keen-eyed (morphs can be played for 2 instead of 3, helps you find creatures with activated ability)

kicker
w u - niambi(bounce to hand: lets you recast morph or kicker)
r g - hallar
g u - varazol
g - verdeloth the ancient (janky saproling tribal/kicker) grunn lonely king (voltron jank/kicker)

cycling
r b - return gy to hand
w b - ravos (return creature from gy to hand) reanimator / gy to hand
u r - draw matters - niv-mizzet/eruth
g b - gy creature # matters: old stickfingers, izoni. storrev - gy to hand
r w - zirda
g u - kydele (add mana for each card drawn)
w u b - sefris - trigger on cycle creatures
u b r - sedris - unearth cycling creatures
b r g - gyrus - reanimate cycling creatures
r w b - alesha reanimate p2 or less cycle creatures
w b g - Teneb (reanimate cycling or morph cards)
u r w - Gavi, nest warden (best cycling commander?) shabraz/ brallin (partner draw matters voltron)
b u g - tasigur (use cycling to fill gy to delve with)
g - jolrael (create 2/2 cats when you draw 2nd card each turn)
u - ghost of ramirez depietro (return to hand a card you cycle the turn you deal dmg with it, morphs can block it, but not much else)

cycling hate commanders
w b g - anafenza (anti-cycling exile opponent gy)
r - zurzoth (create devil tokens when opponents draw outside their turn)

landwalk
u b r - sol'kanar (swampwalk)
b - veldrane of sengir (forestwalk)

landwalk hate
w u - gosta dirk (anti-islandwalk)
b u - ur-drago (anti-swampwalk)
w g - lord magnus (anti-plainswalk/anti-forestwalk)

good stuff
b r - judith (pump creatures, dmg when creatures die)
u r - ludevic (good with morph/combat)
r g w - mayael (p5+ theme works with cycling and morph well), gahiji good stuff (pumps all creatures attacking opponents)
r w b - kelsien, kill weak creatures
wubrg - esika, jodah, kyodai, cromat, garth one-eye, jegantha, the wellspring, o-kagachi

color matters
r g w - rienne, multicolor matters
wubrg - Ramos dragon engine

jank
wubrg - atogatog, korona false god
r- joven

tribal matters
wubrg - morophon (any tribe, humans may be best), sisay (legends matter), niv-mizzet reborn (guilds matter), scion of the ur-dragon (dragons matter)
w b - arvad the cursed (legend matters)

Human tribal
r w b - Jirina Kudro

partners:
u r - ludevic (Morph/goodstuff)
w b - ravos (cycling: return creature from gy to hand) reanimator / gy to hand
g u - kydele (cycling: add mana for each card drawn)
b - Tormod, the Desecrator (gy matters, cycling)
u - ghost of ramirez depietro (cycling: return to hand a card you cycle the turn you deal dmg with it, morphs can block it, but not much else)
u - Sakashima of a Thousand Faces (clone commnader, good in any deck)

shabraz/ brallin (cycling: partner draw matters voltron)

Other cube themes:

Landwalk (unblockable against players playing 5c.)

domain (land type matters, draft when playing 5c for great value)

Kicker

morph

manifest

Cycling / discard matters

Toughness matters:
w u - high alert (defender can attack)
g w - huatli suns heart

colorless matters (use in morph decks to pump them)
tide drifter,

colors matter (Weak in morph decks)
shadowmore lord cycle, transgild and sphinx are all colors,
cards like jaded response, cleansing beam, [[

graveyard matters(best in cycling decks)

reanimator / graveyard value (best with cycling decks)

draw matters (best in cycling decks)

mirrorweave (lets you unmorph all your morphs easily if you copy a card like dragon's eye savants can also stop cards from turning face up if you target something without a morph cost.

tribal synergy in cube:
Human tribal
r w b
wubrg

goblin tribal
r
r b

zombie tribal
b
g b

beast tribal
r g

dragons
wubrg