There's an android app (search for Trakt), something like Trakt Client. You can mark a season and all previous as watched. I've spend a few minutes to mark all my shows watched (I have quite some).

I downloaded the iSeries App (on iOS, idk if its available for android) and linked it with my Trakt Account. In the app you can mark individual episodes or whole seasons as Watched. Syncs perfectly with the website.

You can use this:
Google chrome - Navigate to your tv-show at desired season.
post the code at "inspect element" (right-click)menu item, at "console" tab.
You may insert episodes ids, that you do not want to mark as watched in the first line. (keep the structure)

skip_episodes = [1901630,1989977];
jQuery('#seasons-episodes-sortable > div > .grid-item').each(function(){
episode_id = +$(this).data('episode-id');
if (episode_id){if (skip_episodes.indexOf(episode_id) !== -1){return;}
console.info('dispatch: '+ episode_id);
$.ajax({type:'POST', url:'https://trakt.tv/episodes/'+ episode_id +'/watch',
data:"type=episode&trakt_id="+ episode_id +"&watched_at=released&collected_at=released&force=false",
headers:{'x-csrf-token':$('meta[name="csrf-token"]').attr('content'),
'x-newrelic-id':NREUM.loader_config.xpid,'x-requested-with':'XMLHttpRequest'},
success: function(d){console.log(d);} });}});

We need ability to reset or delete a Collection in one go.
There is no way to select Multiple titles or All and remove from collection which can be huge.

The question can be skipped, you'll need to configure that in your settings page.

Going title by title, clicking watched, then when, then rating it; is very slow and tiring and honestly not very good UX (why can't i skip telling you when i watched something)
It's common practice to allow user to have multiple choice check-boxes and to apply an action to all those selected.

I agree that this would be a great function. Being able to mark entire seasons isn't quite what I want. I often binge watch shows and watch ten episodes in a row, and update my trakt the next day. There is no easy way to mark them. I would appreciate the ability to select multiple episodes and marked them all watched at once (without saying the entire season).

I already works to mark a complete show or a season of show as watched. But what I'm missing is that I can mark them as watched at a specific time.

Usually I don't know exectly when I watched all single episodes so I'd just choose a date when I finished watching all episodes of a season.

Karen - that feature is already present. Once you select the season, there are +Seen, +Collection and +List buttons at the top right.

I would like to be able to add whole seasons without the need to add each episode individually. Similar to how there are eye icons to indicated a watched episode, perhaps trakt can add that for entire seasons, that way we can indicate which seasons we have not watched and which we have. This would be very useful since there are tv shows where I have seen most seasons but not all.

I'd love bulk edit, that is to say check boxes that I can select so to apply any operation to multiple items. That means not just multiple watched/collected, but multiple delete from History too, multiple seen/unseen, multiple add to custom list, and so on. The only case I wouldn't allow multiple operations is Ratings, as you should rate each item one by one.

I would like to see this with movies to.... I reckon they already looked into it, since this is one of the most basic and needed functions in library management and shouldn't be a technical challenge as well with some benefits like better performance to the website do to less actions/requests.

I created images of a proposed design that implements multiple suggested features (almost 2 years ago, on the last feedback site).

You can view the images of the design (& description) here: https://getsatisfaction.com/trakt/topics/watched_show_season_up_to_episode since i don't think this new comment system supports pictures.

A single page which is the merge of the actual "progress collected" & "progress watched" pages (with the same expand/collpase possibilities) but where it's possible to check/uncheck from that page without leaving it.
- check/uncheck collected (per episode, season or for all) ;
- check/uncheck watched (per episode, season or for all) ;
- chech/uncheck new option "TV Show completed" ;
- optionlist with available lists so adding/removing an episode from a list can also be done there ;
- ...

All this without leaving the page and going every time to the tv show page, episode page, ... That's too much time.

You can always remove things from your history page too.

I just accidentally marked an entire series of 100 episodes watched, when I only have watched 18 of them. At present, the only way on trakt to undo that that is can find, is for EACH episode, navigate to their episode page, and mark it as unseen from there.

What should happen, is everywhere you have a "mark watched" - if that button is clicked, it should change to a "mark unwatched".

That's not hard. If people want to mark a program as unwatched, then by definition it does not matter if it is scrobbled or checked in or whatever. Because an unwatched program is none of those.

@beginswithaJ currently, you can remove episodes on an individual basis from their summary pages. If we added a "- Collection" from the season page, would that help? We are also considering adding a similar function to the show summary page for collection.

Watched statuses are more complicated since it can be a scrobble, checkin, or previously seen. Also, the idea is to build a complete viewing history so its not ideal to just wipe out all times something is watched. You can currently remove stuff from your history page and we'll be adding a way to "reset" a show's watched progress to 0% to help with tracking rewatches.

The solution described below are probably (and in my case certainly) good enough for marking a certain season or even a collection of episodes on a batch scale.

However,

A ) there is no intuitive way to manage parts of the library as "(not) collected". This is something I'd really like to be able to do. As I regularly clean up parts of my archive and delete / sell old episodes and DVD's while maintaining the rest of the seasons I haven't watched yet. The workaround of removing a whole show from archive and re-collecting the unwatched material is a pain.

B ) Not everyone as Android for the SeriesGuide app ;)

Yes, I've started using it.

Looks like SeriesGuide does that on a per season level. On the trakt website, you can use the season page for a show and mark episodes watched from there. Just hover over the episode screenshots. Will that work?