Every one said how this Chromanticore could be a pretty sweet Commander, especially considering that it has Bestow on it! How interesting would it be to Bestow this from the Command Zone? To this day, I still wonder about it. But, I'm sure that the Wizards of the Coast design team had their reasons.
Anyhow, Chromanticore is a 4/4 creature with flying, first strike, vigilance, trample, and lifelink. If you Bestow it, which costs 2WUBRG (2 colorless, White, Blue, Black, Red, Green), the enchanted creature gains +4/+4 and all of those abilities. So, on its own or as an Equipment, it's very powerful. If you manage to get all five colors of mana available to you, it's going to be a solid finisher. Then, because it's a Bestow creature, if the enchanted creatures dies or is otherwise removed from the battlefield, Chromanticore remains on the field.
In Standard, it's understandable that Chromanticore didn't do very much. Being a five-color card in an environment where many decks were three colors - perhaps splashing a fourth - didn't really let this card shine. There are ways to sneak it out in Modern and other formats. But, there are such juicier targets to consider in eternal formats that why would you bother?
Although Chromanticore is not a Legendary Creature, some players decided to use it as an unofficial Commander. Decks built around the Manticore have focused on running almost exclusively Enchantment Creatures and other powerful Enchantments. Many friendly playgroups already allow Chromanticore as a Commander, since he's not overpowered. These decks are built purely for flavor, but they look fun. Still, if you're taking the deck to an unfamiliar playgroup, be sure to have a backup Commander on hand, such as Horde of Notions.
Officially, Chromanticore sees a fair amount of play for a five-color card in Commander. Interestingly enough, the Commander who uses the Bestow creature the most is Progenitus, which is odd since you can't attach anything to something with Protection From Everything. Of course, there are other creatures in the deck you can attach it to.
Chromanticore is pretty fun in Child of Alara decks. Attaching the Manticore to it makes for a 10/10 with flying, first strike, vigilance, and lifelink, as the Child already has trample. Karona, False God and Cromat decks also utilize the Chromanticore's talents sometimes.
Honestly, it's a bit strange that Chromanticore wasn't made a Legendary Creature in the first place. The flavor is there. Also, who realistically can play multiple copies on the board at once? You can see why this is an unofficial Commander for some people. It's a casual favorite, for sure. It's a well designed, powerful mythic rare that could have been quite a Commander (officially) if they'd just made it Legendary.
Sure, 5-color Bestow never became a thing in Standard or Modern... But you never know when they'll revisit the mechanic in the future!