Not a cactus, but you're very right is a Euphorbia. I don't think it's E. enopla. Thats a thinner plant. Maybe Euphorbia pentagona:). This is were it gets confusing because I see pentagona and enopla get sometimes confused as the same plant, but enopla I have and is thinner. From what I've read pentagona has 5-6 ribs. Where enopla has 6-7 ribs. From what I can see yours has about five. So I'm going with E. pentagona;). There is Euphorbia ferox, but I have that one and it's more rotund;). Oh ya I have to let you know because I would have a guilty conscience if I didn't. When cut or bump this plant will ooze a white fluid. Reminds me of watered down Elmer's glue. This is toxic so keep off skin and away from mucous membranes:). People have gone to the ER because of this stuff. Where your PPE. There you have been warned;).

Bergzivman, at first glance I thought a Gymnocalycium, but the more I look the more I see a Lobivia;). Sorry not much help, but that's how cactus can be. Sometimes you just have to wait to see what the flowers look like. In this case you would only have to wait for buds to make a ruling if it's a Gymno or not. Gymnocalycium buds have zero spines, fuzz or anything. They're just smooth with a scale pattern;). Very distinct.

Rina. Haha yes I know the flowers are fake, hot glued on , even tho when I bought the plant I thought they were real. I took them off.

Opuntia ficus-indica It will need strong sun to grow nice pads:). Definitely an outside plant if you can.