Wally's death and Artemis's reaction seen on-screen on the Engager is taken directly from the episode "Endgame".
Conner mentions his mission with Dick in the first three episodes ("Princes All", "Royal We" and "Eminent Threat") which was supposed to be a one-time thing. Likewise, Megan notes that they haven't had time together since their engagement in "Princes All".
The Martian blood transfusion that Garfield ascribes as the inception of his powers took place in "Image".
The death of Marie Logan was depicted on page 16 of the tie-in issue "Players, Chapter Six: Rolling Doubles", where Queen Been enthralls Marie to drive off a cliff, after reassuring her that Garfield was waiting there. Garfield's hallucination suggests that Queen Bee was being literal, because he was indeed close to the waterfall looking for Marie, moments before she crashed.
The Doom Patrol Go! series is based on Teen Titans Go!, with all the main cast of that series appearing. Chris Battle, the lead character designer for that show, also designed the characters for Doom Patrol Go!.
Miss Martian's character model is reused from the season 2 episode "Let's Get Serious!", which guest-starred Aqualad, Miss Martian and Superboy.
The Doom Patrol's fate—going on a mission and all dying, with only Beast Boy and Mento left behind and surviving—is similar to the team's demise in Doom Patrol #121.
Lieutenant Tork's "He's dead, Tom" is a reference to a recurring line from Star Trek, "He's dead, Jim".
Gar's line "Whatchu talkin 'bout, monkey?" is a parody of the catchphrase "Whatchu talkin 'bout, Willis?" from the 70s sitcom Diff'rent Strokes.
Monkey cites the "law of conservation of mass" as an explanation to the mystical nature of Garfield's powers, as it states that mass can neither be added nor removed from a system closed to all transfers of matter and energy. Therefore, Garfield would not be able to change into animals bigger or smaller than him, such as an elephant or a roach, without magic.
Do not answer here.
Keep the questions open-ended and neutral: do not suggest an answer.
Garfield: See, I've always thought it would be cool to be on TV like Mom. And for a while, it did make me feel close to her again. Ugh. Or maybe it just distracted me, let me push away the ghosts of her and Rita and Wally, and everyone else I've lost. But I can see now I was chasing a dream, or running from a nightmare, or just feeling the mode. I'm ready to get back to reality, now. Ready to get back to the life.