Here is a screenshot from Dragon Age: Origins. It is plainly transphobic for the implication that trans women are not real women.
As for the scene in DA2, the apparent excuse is that it was an accident and that the writer just forgot to have a response other than “AWKWARD” to Serendipity’s presence. I find that a little hard to believe, but that is the official response, so take it as you will.
However, the following tidbit from David Gaider is worth sharing, from the same BioWare thread that the official excuse for that bit was trotted out.
We love Serendipity. If we didn’t love her, we wouldn’t bring her back for any reason. While I understand someone might want us to have characters that they can personally identify with other than ones that are played for laughs, having a character that we adore and who we think is hilarious is no small feat. I’d hope that she would be taken in the spirit which she was meant.
Here, we have a cis writer excusing the game’s general handling of trans women with, “But we LOVE Serendipity! She’s hilarious!” Such a response paints Gaider as really insultingly transphobic himself.
There’s also the issue that the only trans women present in BioWare games are sex workers. Relegating trans people to only that role plays into a lot of transphobic bullshit, but the long and short of it is don’t reduce trans women to sex objects you bigoted fucks.
One last detail is something I myself am trying to find out. I would like to find out who voiced Serendipity. If it was a trans woman, then great! That would be the one thing BioWare hasn’t handled horribly in this whole mess. The alternative is that there was a cisgender voice actor trying to sound like a masculine voiced trans woman, which would be insulting as fuck, because it would be a member of a privileged group mimicking a bigoted stereotype of an oppressed group. I do not have faith in the game industry or in BioWare sufficient to simply assume they did the right thing here, but I’ll hold off on outright calling them awful for this one particular element amongst a lot of existing awfulness until I have more information.
Short Version: BioWare produces incredibly transphobic media and all the excuses in the world don’t change that, especially when one of those excuses show just how bigoted and ignorant the person giving that excuse is.