Alright I just did it as Doomsday and first of all I did what TheMajinLegend mentioned and deleted the download of the update since Doomsday got nerfed. I prefered the combo (down a, x, x, down foward y) rather than (down a, a, a). The second one left too many openings for me and I can start the combo immediately the other way. If they block however u want to do down a on the ground to trip them up, then start the combo again. Most of the time u will. There are however some enemies that u are better off doing the infinate combo over and over. I'll mentioned some key opponents as to which method is better. Without further adu, here is the list and the keys I will be using is:
Combo Trip= (down a, x, x, down foward y then down a)
Combo 2 = (down a, a, a)
Combo Death = (down a, x, x,x down foward y constant)
Avoid = (Matchup really bad)
Aquaman: Combo Trip
Batman: Avoid, this is one of the ones I didn't fight, but would rather not since he has answers for everything
Black Atom: Either Combo Death or Trip. Best matchup
Catwoman: Combo Death
Deathstroke: Combo 2, this was the only matchup I did that. Worked better.
Flash: Avoid, 2nd worst matchup
Green Arrow: Combo Death, get close too, big spammer of arrows.
Green Lantern: Avoid, worst matchup needs to be banned from max.
Harley: Combo Trip
Hawkgirl: Combo Death
Joker: Combo Trip
Killer Frost: Either Combo Death or Trip
Lex: Avoid/Either. I beat him, but was extremely risky. rather avoid.
Nighthawk: Combo Death
Shazam: Combo Trip
Sinestro: Combo Death
Solomon Grundy: Combo Death
Superman: Combo Trip, ppl says avoid, I say don't. was very easy for me.
That is all I have character-wise for now. BTW the only time I used the meter was to use supernovas to finish a bar/kill, Clashes (I liked this a lot) to prevent combos at near death, and only use supermoves when stuck in a corner. Doomsday does enough damage, would rather use it for clashes and finish off my opponents. Sorry I only had 3/4 of the characters, but I don't feel like figuring out everyone for now. If I feel like it, then I let u know asap. GL