Mr. Reachy is first shown being retrieved from the Panic Room by a frightened Dean Venture, who reassures him "It's OK, Mr. Reachy. Brock will be here soon and everything will be fine." Dean clutches the stuffed animal to his chest as he crosses the laboratory, then inadvertently flings Mr. Reachy behind him in shock when he discovers The Monarch forcing himself sexually on the robot G.U.A.R.D.O.
When The Monarch successfully raids the Venture Compound--which, unbeknownst to him, has already been vacated by the entire Venture family under the mistaken impression that the O.S.I. is trying to kill Venture bodyguard Brock Samson--he sends the Murderous Moppets Tim-Tom and Kevin to the boys' bedroom to subdue Hank and Dean. The Moppets cut a hole in the lid of Dean's learning bed and Kevin dives inside with his switchblade, only to emerge with a puzzled expression on his face and a badly damaged Mr. Reachy in his right hand. The stuffed animal leaks stuffing from the numerous gashes Kevin has inflicted on it with his knife. Kevin wonders aloud what a teenager would be doing with a stuffed animal. Tim-Tom replies that he knew what he did with them and Kevin agrees he did the same, reflexively dropping Mr. Reachy to the floor in disgust. "Ugh! I can't believe I touched it!"
Mr. Reachy is next seen being toted around by the malformed Dean clone D-19, who keeps the stuffed animal amongst his possessions in his secret attic bedroom in the old Venture Apparel Division. Somebody--presumably D-19--has sewn up all of the gashes left in the stuffed animal by Kevin's switchblade as there are visible stitches of a different thread color on Mr. Reachy's outer fabric. D-19 hallucinates the voice of his father, Dr. Venture, chiding him for being too old to sleep with a stuffed animal and urging him to return Mr. Reachy to the "real Dean."
Dean dyes his hair and starts dressing in a black speedsuit as part of his decision to leave his childhood behind. He drags his learning bed out onto the lawn of the Venture Compound, douses it with gasoline, and sets it on fire. Dean tosses several items from his childhood on the blaze, including a sweater-vest, his Bizzy Bee wallet, and one of his Giant Boy Detective books. When he pulls Mr. Reachy out of the box of childhood memories, he stares at the stuffed animal with a quivering lip and a tear in his eye. Dean gingerly touches the stitching where the stab marks in the fabric had been repaired. He hesitates, dropping the stuffed animal to his side instead of throwing it on the fire.
After Sergeant Hatred and the Order of the Triad fail to prevent the Venture Compound from burning to the ground, Dr. Orpheus attempts to comfort Dean Venture at his uncle Dr. Jonas Venture, Jr.'s funeral: "I know how much the little fellow meant to you, young Dean. And that is why, against my better judgement and at great personal risk I decided to use all of my mystical powers...to save him." Orpheus then presents Dean with a singed, soot-covered Mr. Reachy.
When Dean moves into his dorm room at Stuyvesant University, Mr. Reachy's head is poking out of the top of the first box he carries in. The doll's button eyes have apparently fallen off and only X marks remain in their place.
- In the season 6 premiere Hostile Makeover Hank buys Dean an adult giraffe as a present, which Dean names Mr. Reachmore.