"When the host of the show pretends to be there for everyone but actually just cares about the interests of the show and what will make USA the most money. #dramasells #thanksforthesupportmark," Casey, 26, tweeted.
Casey continued to slam Mark by writing on Twitter, "My boy Mark always supporting! He's a joke and this show is a joke. #manipulationisland #sueme."
Laced in between Casey's posts were screenshots of controversial tweets Mark, 57, had liked on Twitter.
One of the screenshots was a GIF of a clown that was supposed to represent how Casey looked after his emotional breakdown over girlfriend Ashley Howland hooking up with a single considering Casey had previously insisted he'd be fine if Ashley left him.
Another screenshot showed Mark liking a meme in which a Twitter user wrote, "When a weak woman turns strong and a cocky man turns weak. Casey can take his fake cryin frat boy ass home! My girl Ashley FLOURISHING !!!"
Casey also retweeted comments from fans who slammed Mark on their own.
Casey retweeted someone's claim Mark "is a company guy" who "probably doesn't like it that Casey is mouthing off about the show and criticizing it heavily. Mark is siding with the ones who give him a paycheck."
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Evan also defended Mark on Twitter and wrote to Casey, "Leave @marklwalberg outta this. That's my guy. Take the L and get off your phone. We all know Mark has our best interests. If you had something important to say you would have showed up to the reunion..... #twitterfingers."
Casey just replied, "Lol," to Evan's tweet.
"Don't get it twisted," Evan added, "this has nothing to do with money. You're the one getting butthurt on our Hosts LIKED tweets and screen shotting them. Like I said, don't come for @marklwalberg. #pickyourbattles."
Casey then responded with, "Why are my battles any say of yours? Oh wait they're not, get the f--k out of here," later adding, "What a stand up guy! Leave it to a cheater to say such kind things! Gives me hope that there still is good in the world. #usanetworksbitch."
Back on November 21, Casey also ranted, "Got about 300 Instagram messages in the last hour of people calling out Temptation Island production for blatantly manipulating people instead of presenting the truth. Keep em coming #thisshowsucks #whatajoke."
Temptation Island has featured Casey and Ashley's relationship of a year-and-a-half falling apart at the seams because Ashley appears to be falling for single Ben Knobloch.
Ashley, 25 -- who was completely smitten with Casey in the beginning and sold on the idea of staying together -- only decided to give Ben a real shot on Temptation Island after she watched a video clip of Casey allegedly telling a girl that he'd be totally fine if Ashley chose to leave him and he wasn't sure how much he truly loved her.
Casey was also shown saying he'd just continue partying and hooking up with random girls if he became single again, which was a life a big part of him missed.
As a result, Ashley went on a date with Ben and made out with him. Later that day, she welcomed Ben into her bed so they could continue their steamy makeout session while Ben was lying on top of her.
Casey was forced to watch the intimate footage of Ashley and Ben at a bonfire meeting, and he burst into tears and punched the bench he was sitting on multiple times in pain and frustration. Casey lamented how he regretted ever asking Ashley to go on Temptation Island with him.
Ever since then, Ashley has been opening up her heart to Ben, suggesting he's a better overall catch -- and kisser -- than Casey.
Casey, however, is claiming production spliced his words together for dramatic effect. He said the footage of him seeming nonchalant about his future with Ashley was "choppy sounding" and "cut" in that his words didn't even match the movements of his mouth.
While fans have yet to find out whether Ashley ended up with Casey, Ben or no one, a source toldUs Weekly that Casey did not show up for Temptation Island's reunion special this season, as Evan had mentioned in one of his tweets.
Us reported earlier this month the reunion taped in early November in Los Angeles and was "explosive."
"Everyone knows that Mark cares a lot about the men and women on the show and only wants what is best for them. As far as Casey is concerned, no one really understands what is going on with him," the source told the magazine.
"He didn't show up at the reunion and if he had, he would have been given ample time to speak his mind."
As for Mark, he apologized for liking unflattering tweets about Casey and his relationship with Ashley.
"I truly apologize for liking a meme that was insensitive. that's on me. it was not on purpose. I meant no disrespect to Casey and completely understand [sic] why he'd be angry. I'll pay closer attention going forward," Mark wrote on Tuesday.
"I often 'like' nearly all show related tweets. sometimes without really paying attention. I click 'like' on the ones that are 'mean' to me as well. I meant I wasn't agreeing with the meme. For the record, I like Casey very much and completely respect his feelings."