The last review of SEA Source was over five years ago. A lot of things have changed since.
The most notable drawback of SEA Source is its trace requirement. For one thing, you have to be at least as rich as the Runner to land the tag. Perhaps more importantly, landing a guaranteed tag will set you back a number of credits equal to the Runner's credit total. So if you're playing SEA Source, you need to meet one of two requirements: either
- Getting a tag mid-turn is valuable enough to your deck that it's worth paying any number of credits to pull off the tag; or
- The runner is currently so poor that the amount you're paying for the tag is reasonable by comparison.
Traditionally, SEA Source was only played for the combo with Scorched Earth, giving you 4 meat damage on the spot (8 if you had a second Scorched Earth, almost always enough to kill). That fulfils the first condition above; as long as you have enough credits to play the Scorches, it didn't matter how much you spent securing the kill. But Scorched Earth has rotated, and its primary replacements (BOOM! and High-Profile Target) seem to have been designed specifically to prevent the SEA Source combo working. BOOM! requires two SEA Sources and is a double (thus you'd need four clicks to pull the combo off, making the combo unreliable and expensive to set up in both credits and influence). Meanwhile, a single SEA Source tag will do only two damage when combined with High-Profile Target (four when combined with two High-Profile Targets), which is going to be survivable for most runners (additionally, influence constraints mean that you can only really do this in Weyland).
As a consequence, after losing its main combo, SEA Source ended up dying out in favour of alternative tagging cards: first Midseason Replacements, and when that rotated, Hard-Hitting News. But it nonetheless isn't a bad card, and as such it's made something of a resurgence lately, as a sort of "alternative" tagging strategy.
Nowadays, SEA Source is primarily played as an enabler of single-tag punishment cards, taking advantage of the fact that it lands the tag mid-turn and gives the Runner no clicks to react before you use it:
- Exchange of Information is the closest comparison to the old Scorched Earth combo, potentially giving you an immediate win by swapping a 1-point agenda for a stolen 3-point agenda (and thus making SEA Source's credit expenditure redundant). It's a lot fairer (read: less broken) than the old tagging combos were, because you need to be playing a mix of agenda sizes and will need to be on 5 points already to close out the game. That makes this an unpopular strategy, but it's still seen from time to time and can be effective, often as a plan B in a deck whose primary strategy happens to use some of the same cards.
- The All-Seeing I has an effect that is incredibly powerful against some decks; if you can land SEA Source into The All-Seeing I against a runner with a resource economy, or an early-game Adam: Compulsive Hacker, the runner may end up unable to execute on their strategy. There is some number of credits at which doing this becomes a bad idea, but it can be fairly high; as long as the Runner isn't super-rich, spending to pull this combo off may well be viable.
- The best combo, however, is probably with Closed Accounts. Landing a SEA Source loses the corp a number of credits equal to the number the Runner has. Then the Closed Accounts follow up loses the Runner a number of credits equal to the number the Runner has. In other words, both you and the Runner lose the same amount of credits, so unlike the other uses of SEA Source, this isn't setting you back relative to the Runner. If you do this on the first two clicks of your turn, you have one click left to make use of the tag, too; The All-Seeing I or Hard-Hitting News are both great options to make use of your (effectively) free tag, or perhaps you could simply trash a resource with your leftover credits.
These are all cases in which you might viably want to pay to land a tag on a rich runner (richer than around 12 or so), even though you have to match the size of their credit pool. Despite working better against a poor runner, SEA Source is nonetheless typically only used in decks that can't reliably keep the Runner poor; if you want to land tags on a poor runner, Hard-Hitting News is usually better. Of course, you could run both (they even combo with each other if you're running Closed Accounts), and many decks do. SEA Source also has the advantage of the surprise / deck-building factor; some tech cards against Hard-Hitting News (notably Misdirection) have no value against SEA Source because they require spending clicks to use, and the Runner doesn't have clicks during the Corp's turn.
If you're unfamiliar with tagging suites, one warning: "I'm richer than you" tagging suites tend to accumulate in your hand over the course of the game, because you often won't draw them when you have a tagging window and/or won't have a tagging window when you draw them. If you have a strong economy (and you need a strong economy to play them), the window will likely come eventually, but you don't want to clog up your hand for too long before then. As a consequence, cards like SEA Source, and the corresponding punishment cards, are rarely played as 3-ofs; playing more than 1 or 2 is generally not worth the deck space unless your entire deck is critically dependent on landing the tag (and given the "soft" nature of SEA Source's tag punishment companions, it almost certainly shouldn't be).
In conclusion: if you're running a deck that can easily get rich, but can't keep the Runner poor, and are looking for a tagging suite, SEA Source, while well short of its former glory, is still a viable option, and can surprise a runner who is trying to play around Hard-Hitting News but feels safe in running once they have 12-15 or so (the point at which Hard-Hitting News becomes uneconomical). It might not get you an immediate flatline any more, but can nonetheless win games, typically via ruining the Runner's economy in combination with NBN tag punishment. So it is once again seeing some play, and rightly so.