Awesome Art: The characters from Ōkami all look more vibrant and more realistic here than in the style of their original game.
Awesome Music: The soundtrack for the game consists largely of epic Orchestral Bombing arrangements of each character's theme song. Have a listen to the themes for Ryu, X, Wesker, and Nero.
Chun-Li's hero art Yawn couples units with the Ascended mechanic introduced in The Force Seekers, which allows players to spam units in quick succession in order to overwhelm their opponent by using Yawn on a unit and then sacrificing it for a unit with Ascended by instantly gaining 4 MP, allowing powerful units to be summoned or replaced extremely quickly. Due to the overpowered nature of the hero art, Yawn's AP later increased from 15 to 20, which means that the art won't be used multiple times.
When Zero was first introduced, his hero art Rakuhouha encouraged players to spam low cost action cards as much as possible in order to build up their memory count for the art, which allowed them to wipe out an opponents entire board with enough build up.
The Astalos unit seemed innocuous at first, but Black players quickly found out that its low 3MP cost meant it could be brought into the game with relative ease and returned from the graveyard with cards such as "Hatred Reborn." This, coupled with Astalos' Resonate granting it +1 attack meant that it was very easy to build extremely powerful Astalos' across the board and bring them back the moment they were defeated. Abilities such as Akuma's Ashura Senku made it even harder to remove these powerful units. Astalos was changed to gain +1 attack for only one turn and the resurrection action cards Hatred Reborn and Warped Research Instinct now inflict seal on the units returned to the field, preventing this unstoppable tactic.
The X unit introduced in Haunted by Memories had the resonate ability that granted every friendly unit +1 health. This seemed decent at first, but when placed alongside multiple versions of the unit it had the effect of stone walling opponents. That still wasn't too bad, until it was coupled with X's hero art Charge Shot, which gives units the ability to gain +1 attack every time their health is increased, meaning the units could become incredibly strong tanks with very little effort. This was nerfed with the Version 2.5 Update, which prevented the unit from increasing its own health through resonate, making the strategy less effective.
Capcom released a similar online card game based on Street Fighter V called Hado Stone on April Fools' Day, a year before this game was announced. Before that, some of the playable characters from SFV (including two of the base-launch heroes, Ryu and Chun-Li, along with Cammy, M. Bison, Juri, Vega, and Karin) also appear as Leader skins in a similar online card game called Shadowverse.
The Mysterious Girl is indeed Ada Wong, and she's later confirmed to be the new Hero on March 2021.
Many assume that the game would get new heroes from unrepresented IPs joining post-launch in the future, which was later confirmed on September 2020 with Amaterasu from Ōkami joining as a hero on the following month.
At least one redditor was able to predict that Oichi would be the next hero after Amaterasu before it was confirmed after the WC2020 Finals. It's more of an unexpected pick compared to previous post-launch heroes.
Dante is consistently considered one of the weaker heroes across multiple updates, While his hero arts aren't as bad as others, that are beneficial outside of specific scenarios or setups, and are overall middling compared to all other heroes. The main exception is Devil Trigger, as the ability to negate all damage for a short amount of time has many uses, and it's low cost makes it easy to build up and use quickly.
Rathalos is considered particularly bad, with his hero arts being difficult to effectively use and being considered less effective than other heroes.
They Wasted a Perfectly Good Character: Morrigan here is portrayed once again as an evil monster. This disappointed fans of her, who would have preferred her to be like she is in canon, friendly to others like as well as not have to killed humans.
Rather "Unexpected Character Design", but Dante using his incarnation from Devil May Cry 4 in this game instead of his iconic Devil May Cry 3 design or even the newest incarnation from Devil May Cry 5, was quite a shock to many fans, despite being the first crossover game to use the DMC4 design as his default appearance. That said, while Dante not using his DMC5 design is due to said game being announced a year after TEPPEN started development on 2017, it would be too early for the dev team to put representation from a game released on the same year as TEPPEN at launch.
Minor example. The Day of Nightmares expansion features the presence of the characters originating from Resident Evil: Operation Raccoon City, despite being an unpopular RE spin-off compared to other games like The Chronicles series.
Many do expect Akuma to be playable despite being a black hero and Street Fighter already having two heroes Ryu and Chun-Li, but the previous two expansion heroes Jill and Nero are respectively Red and Green and built up the representation of the series that only had one hero in the game's launch, with many expecting for the next hero to be a purple one coming from Mega Man or Darkstalkers instead.
Like the above and on the topic of a new purple and Mega Man hero, Zero is also expected as well, but despite already appearing as a Unit Card due to Jill and Nero previously appearing in Action Cards but didn't have Unit Cards featuring them before their inclusions and Akuma not making any cameos in the game before his inclusion, many wanted Sigma, as he previously appeared in a few Action Cards despite not having a Unit Card based on him instead before receiving a Legendary in Zero's expansion.
Breaking trends aside, Oichi, the sister of Oda Nobunaga, surprised many, as no one expected for her to be a new hero due to Sengoku Basara's popularity in Japan and said series' inclusion as usable cards in the previous expansion. Despite Oichi being an supporting character to the plot, many wished for major characters from said series like the aforementioned Nobunaga, Yukimura, Masamune, Ieyasu, and Mitsunari to take her place to represent that series instead before they received legendaries.
The Operation Cannon Spike focuses on the video game of the same name, and includes with it the game's Original Generation characters Simone and Shiba, as well as two boss characters, Beauty and Kabuki. Somewhat downplayed in that at that point Cammy was recently Promoted to Playable (as an EX skin) but it's still highlighting a somewhat-obscure game and characters.
The Sigma's Invasion adds as an ally to Sigma the Master Computer Akatsuki, aka the girl on the title screen of crossBeats Rev., an obscure arcade-only Rhythm Game that was taken offline in 2018.
The Turnabout Festival expansion adds in Fiona Belli and her dog Hewie, and not even as a central focus of the expansion's narrative. More egregiously it also includes Keyboard Mary from Otoranger, Capcom's other obscure defunct Rhythm Game (and a Japan-onlyMobile Phone Game no less!).
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