Units you forgot were even in the game?

Arden and zephiel... they just not better than my zelgius.
narcian faded as well

Clive. When was the last time you saw him in Arena or Grand Conquests or anything? Pretty much most Tempest Trials units that aren't Black Knight and Marth seem to be benched.

If there were any units that I forgot, then I wouldn't be able to answer you because I forgot about them. lol

Now, I'll try and give you a unit that I think is forgettable. And as much as it pains me to say because I really like this character in Shadows of Valentia, I am going to have to give this (dis)honor to Clive:

As one of the early Tempest Trial reward units, Clive isn't that great. His base kit contains Silver Lance+, Escutcheon, Def +3, and Hit and Run--all of which are either bad, niche, or available on other units. You can't really make good use of him out-of-the-gate or fodder him off for anything good, and he requires a ton of investment to make him decent.

Clive is also a Blue Lance Cavalry unit, which is pretty crowded as is. Offensively, he loses out to units like Peri, Oscar, and Roderick who have a much better offensive spread than he does, while also having access to merges and IVs. Defensively, he loses out to Camus who has higher Spd to avoid doubles and a DC weapon to retaliate at range. I'd argue that even Berkut is better, despite not being that great himself and having slightly lower Spd, Def, and HP, because he has his Berkut's Lance and Water Boost at base and has access to more merges than Clive. But even when compared to the other Blue Cavalry units, you got Reinhardt, who most people would prefer to run as the Blue Cavalry unit of choice because of how powerful he is with so little investment.

Luke

I've never seen him as anybody's unit in the friend list and never gotten him either

no prf also means his kit stays silent

Tobin, never got him from the TT and forgot that he even existed.

I won’t lie, sometimes I forget about Celica...
lol

Tobin. Doesn't help that they made him a generic forgettable sword user instead of his canon class.

I also forgot Saber was in the game until recently. He's rare enough that I've never summoned him and no one who has him seems to use him since there are so many flashier sword users. It's really too bad because in SoV Saber was pretty bomb.

Navarre. That guy just disappeared...

I constantly forget that Lachesis is in the game. I like her from FE4, but in heroes i never summon her and she’s just so bad and irrelevant

Tobin and, quite sadly, Seth.

Yup, those with awkward fodder units that show up when you least expect: Raigh, Odin, Mathilda, Clair, the White Wings, Cherche, Caeda, Jagan, Gunter, Raven, Serra, Clarine, Ogma, Lachesis, Marth, Roy, Seliph, Peri, Hana, Fir (aka Frida Kaelo), Stahl, Donnel, Wendy, Seth, Luke, Roderick, Jorge, Cordellia, Virion, Setsuna, Niles, Jakob, and Kaze.

I would seriously favor giving all of these a alternate as their new "base model" and removing their original models from the game. A lot of them need new/better art (shave Fir's unibrow) as well, so they aren't so disappointing to get, especially if you're someone like me who doesn't know them from their original games.

And I legit forgot about Fartre/Barftre/Bartre cause he just needs to not exist anymore in any game.

Man Marisa is so good. I used her a bunch right after I got her. Gave her a wo Dao refine and evereverything.

Then I started trying to build other reds for diversity and yeah... Haven't used her since. Haven't forgotten about her. But haven't used her.

Kellam.

I haven't been in the game ling enough to barely know anything about Tobin or Clive, but Lon'qu seems like a forgotten unit. People say he used to be popular.