After watching some episodes of Jojo's bizarre adventures I what my Omni Ben's Stand would be. And here is the result.

Name: Emerald Rex
User: Ben Tennyson
Card: the T-Rex
Powers: able to take on any powers it sees, be it from a Stand, Alien, wizard or anything. Also capable of being seen by others if Ben wants.
Acquired Stand powers so far: Magician's Red, Star Platinum, Purple Hermit, Silver Chariot, Hierophant Green, Hanged Man, Dark Blue Moon, Golden Tempest. (Able to acquire more in the future)
Weakness: no displayed weakness, however if user isn't able to witness a power, can't use the power.
Other information: has already acquired his user's abilities through viewing his memories, has a brother Stand named Draco Scarlet, combined Star Platinum's Ora Ora Ora move with Armadrillo's fists to create maximum damage shockwave punches.