Doomsday is required for all matches of challenge battle 5. There are three possible characters you could choose: Doomsday/Regime, Doomsday/Prime and Doomsday/Containment. While Doomsday/Regime is given by the Starter Pack, he is a silver card and thus has much lower stats and he has a poor passive. Doomsday/Prime is a very strong card especially for new players, and he is always available for purchase (while Doomsday/Containment can only be found rarely in Challenge Booster Packs and the Most Wanted Pack. If you didn't unlocked him in his challenge from over a year ago; it is not practical to try to get him solely for this challenge). Therefore, Doomsday/Prime is the best choice for this challenge battle.
Challenge battle 5 is generally regarded as the hardest battle on standard difficulty. It can mostly be done with normal gold cards (without promotions or good gear), but it will take a lot of practice and luck.
There is a bug where the first match would display the opponents from the second match.
Teen Titans Cyborg regenerates health whenever he is tagged out. His s1 is a stun, which means it deals only half the normal damage (but remember to block it or you may be stunned). Both of this and his low damage stat encourage you to allow Cyborg to be in the fight and let him hit you to gain power. Regime Wonder Woman generates a small amount of power whenever she blocks an attack, so it's best for new players with no basic damage gear to just let her hit you so you can get power quickly. As always, look out for Doomsday. His s2 is quite fast, and he heals by 50% of his maximum health when he knocks out an opponent; however, since this obviously as no effect when he is already full, you could opt to sacrifice a character at already very low health to take that hit when he first tags in (2 characters with high health is safer than 3 characters with low health against Doomsday).
This fight can be a bit of a drag, as Man of Steel Zod and Red Son Green Lantern have decent health and their passives further reduce special and super damage by 20% (Green Lantern is additionally immune to stun and crit), and Arrow Green Arrow has a power drain s1. They don't do much damage though, and shouldn't be too hard, just time consuming.
Regime Aquaman's passive doesn't work here, but remember to tag out your character immediately after he uses his Trident Toss s1 to avoid the damage over time (and +20% additional damage taken from all sources while the bleed lasts).
Regime Black Adam's Lightning Shield is more than just annoying - it reflects twice the damage of special 1s used against it (and 75% of anything else), so you will kill yourself very quickly if you use your character's special on him while his shield is active. Pop the shield (lasts 3 hits) with basic attacks (but be careful and ready to block his specials if applicable), then destroy him with a super when it is down. An unexpected danger is when you are about to use a super, but Black Adam tags in at that moment to take the hit and you will take 75% of your super's damage, which could be devastating. While tagging is somewhat unpredictable, the first character (Regime Aquaman in this case) tends to tag out when they reach 50% health.
Krypto Lex Luthor is a powerful support with his frequent and strong s1 power drains, and his passive gives his whole team +30% maximum health.
Easily the hardest fight yet. Regime Killer Frost reduces all healing by 90%, which is crippling to any card with good healing - particularly the very Doomsday that is otherwise the best candidate to this battle overall, with great strength (especially to new players) that comes from his huge heals. In the very unlikely event you have Containment Doomsday, he is a much better character in this match as his resurrections are not affected by her passive.
Similar to Regime Aquaman, Batman Returns Catwoman's s1 causes her victim to bleed - which is worse here since Chaos prevents you from tagging out at will. This issue also make Regime Killer Frost's s1 (attack speed and power generation slowed by 50%) and Insurgency Joker's s2 (-20% damage and poison damage over time) harder to deal with.
Knocking out Insurgency Joker causes your character to lose 40% of their maximum health that can't be avoided or reduced by most means, especially painful when Regime Killer Frost's debuff. Try knocking him out with a character who already has very low health, since this can't knock them out. They will stay at 1 health, and can still be used to tank a special.
Doomsday is significantly more dangerous to fight when he is the first character; since the first character usually tags out at 50% health, it gives him a very good chance to wait for two bars, tag in again to knock out one of your characters with Earth Shake to recover almost all his health.
His two teammates are also notorious for dangerous bursts of damage: Luchador Bane has a high chance of an unblockable stun when he tags in and also gains 25% damage; Green Lantern Sinestro's next special gains +50% damage if you tag out against him.
For Luchador Bane, be ready for his tag in when Doomsday reaches 50% health. After that, knocking out a previous character with a special rather than a super or basic attacks will negate his tag in stun.
Avoid tagging out against Green Lantern Sinestro, unless you have s1 power draining character who can keep his power under 1 bar.
Batgirl gives her team a bar of starting power each, and Arkham Harley gives them +25% maximum health, making it an uphill battle. Arkham Harley's s2 allows her to throw an unblockable bomb, heal or damage buff her whole team, so it is somewhat luck based.
Raven's passive is exceedingly dangerous to those who come unaware. She swaps health with her opponent when she falls under 20% health, twice per match. Using a super move when she's 30%~40% is an excellent way to get rid of her safely. Doomsday's special 2 could also be used, but there is always the risk of it being blocked and not quite finishing her off.
Challenge: Countdown! (You must defeat your opponents within 3 minutes)
A somewhat difficult fight, as you only have 3 minutes to beat the enemy team, which is well suited to dragging out the match. Zod has high base health, and he heals by 20% and gains 20% damage per teammate knocked out, but Containment Doomsday is the real problem: his passive resurrects him 3 times, giving him 50% health and power each time as well as a stacking +10% damage increase. This gives him an effective health of almost 15k and additional great damage absorption potential as the hit that triggered the resurrection will not roll over to the next "life".
Countdown will continue to run as normal during a special, causing specials to eat up a lot of precious time. On the other hand, while supers do not cost any time, the high single hit damage becomes less effective against Containment Doomsday's passive.
Blackest Night Batman gains 20% damage between midnight and sunrise (0:00 - 6:00). You can chance your device clock's time to outside that range if needed. Blackest Night Batman has since been updated, but it is unknown if the challenge will return or if it will use the same characters.
Aquaman has a bleed on s1 that could be avoided by tagging. His s2 summons a soldier to fight for him instead. While the soldier can do slightly more basic damage than Aquaman, he can't use specials and Aquaman can't gain power while he is active. Additionally, knocking out the soldier will also count towards Doomsday's Hero Killer Passive, healing him by 50%.
Arkham Origins Deathstroke has a chance for his s1 to be unblockable and crit, which can do quite a bit of damage.
Elseworld Flash slows his opponent and disables their specials and supers when he falls below 30% health. Red Son Wonder Woman and Solomon Grundy gives the whole team +30% power generation and health.
Red Son Deathstroke gives the team +10% speed, Grundy +30% health and Animated Harley Quinn +20% power generation and damage, in addition to the team heal/team damage boost/unblockable bomb s2 like all Harleys.
Challenge: Dampening Field! (You will generate power at a reduced rate)
A bit of a luck-based match.
Man of Steel Superman has a 30% chance of not using power on a special.
Zatanna's s2 can either give her a 50% damage boost, power drain, deal additional damage over time, heal herself by 50% of maximum health, or stun herself. Forcing her to tag out will remove the damage boost.
Martian Manhunter's light combos can deal damage over time, stun or power drain, making it dangerous to let him hit you to generate power. For this reason, try to drop hard-hitting specials/supers on him quickly to avoid tangling with him for too long.
Another challenging fight. Cassandra Cain is a swift and brutal combatant; you lose 25% of your current health whenever she tags in, and her s1 has a fast animation, so be very careful and be ready to block. Her very high damage is further increased by 600 Wonder Woman's team wide buff (+30% damage and power generation to female teammates), allowing her s1 to hit over 7000 damage and knock out most normal gold cards under level 30 in one go.
Batman Returns Catwoman greatly increases damage over time effects by her team, causing her s1, as well as 600 WW's s2 (which is quite likely as she is the last opponent), to do a lot of bleeding damage, and the bleeds will, as usual, cause you to take 20% more damage. This also increases Cassandra's tag in damage to 30%. Tag out your character immediately when hit by a bleed. Credits: 510
Try to knock out Boss Solomon Grundy quickly instead of letting him stay at low health, as his basic attacks gain exponentially more damage the closer he is to defeat. At critically low health, his heavy basic attacks can do 1663 damage (or almost 5000 with a single heavy combo, easily half of a normal gold card's maximum health).
Assuming equal stats, Containment Doomsday is a stronger option here as Doomsday's passive is useless on a single boss. His resurrections are also ideal for absorbing Godfall Superman's one-hit 7000+ damage Flying Punches. However, as stated before, it is not practical to try and get him solely for this challenge.
While there are no handicaps (the Regeneration handicap is part of what made the Martian Manhunter challenge boss so difficult to beat), Godfall Superman still has a huge amount of health for new players; easily taking 5+ super moves for normal, non-elite gold cards. He also have a good amount of damage; his basic attacks can hit almost 500, making it very difficult for normal gold cards to win this match. Even if you managed to go through the rest of battle 5 with a normal gold team, you'll likely need to pay 30,000 credits to skip this match.
As he has high health and is not accompanied by other characters, cards dealing % maximum health damage (The Joker/Prime, The Joker/Insurgency, Raven/Prime, Batgirl/Cassandra Cain) is very effective. Out of those, Insurgency Joker is the most practical; he is a common drop from Gold Booster Packs (so new players have a decent chance of getting him) and is significantly stronger than Prime Joker. While Raven and Cassandra Cain Batgirl are much stronger, they are much more difficult to obtain, especially the latter.
Godfall Superman will cause him to take further halved basic damage while he is blocking and reflecting the other half back to you. However, this grants you a lot of power, so it is actually advantageous to you if you can get him to block your basics (which won't do too much damage to you if you are a new player with barely any gear, or just focus on non-basic damage gear).