There are a lot of variations for these:
KC,KC,Monument, militia, masq and nothing else.
Each turn nets you three points and trashes the other guy's hand (completely) and deck (eventually). Once this is set up only duration or reaction cards (notably moat and less notably horse traders and tunnel) can stop it.
Slightly fewer points per turn, still destroys the other guy's deck - but is only a 3 card combo - KC/KC/goons/masq. Once you destroy the other player's deck, you can buy one copper, masq it over, trash whatever is passed back to you, and trash your copper when it comes back. You can keep this going until you run out of 6 coin (or less) cards to buy & burn.
KC/KC/militia/masq/bishop will likely eventually work. Late game you have an opponent with a deck consisting of nothing (having used KC/KC/militia/masq), you buy a bishop, and they buy a copper. You play KC->KC-> militia -> bishop your masq (+2 points) and then bishop nothing twice (+2 points), you buy a masq. They buy a second copper. You play KC/KC/militia (like normal) and then triple play the masq. You pass your bishop, and trash one copper. You pass nothing and trash a second copper, you pass nothing and trash the bishop. You buy a bishop and repeat the cycle. Eventually you will run out of bishops or masqs but is awfully hard to sock away 40 or more points with bishop before I can pin you (especially as I can trash estates & coppers whenever you use a bishop)/
This is the strongest simple pin attack of which I know, but it has no innate VP gain. If there are no chip gaining cards, native village, or islands this will almost invariably win once you hit it (you can pile copper & curses estates late game after a very long time & win).
KC/KC/masq/nobles/outpost
Play as:
KC -> KC -> nobles (do whatever) -> Outpost -> Masq (trash 3 cards from their hand/deck).
KC/outpost stays on the board
Play outpost turn as:
Nobles (actions) -> KC -> masq (trash 2 cads from their hand/deck)
This cannot be defeated by reactions (tunnel, horse traders, moat) and burns through decks quicker if the opponent is doing something like double tactician with card gainers or scrying pool/haven to try to prolong the game.
The strongest combo I know is:
Scheme/masq/outpost/monument/KC/KC/KC
Play this as: KC->Scheme-> KC -> KC -> outpost -> monument -> masq. Net results - burns 3 cards & gains 3 VP.
Return to the top of the deck KC/KC/Scheme. Keep on the board KC/outpost.
Outpost turn is played as KC -> KC -> Scheme -> monument -> masq. burns 2 cards & gains 3 VP.
Return to the top of the deck KC/KC/Scheme. Total gain all 5 cards burned from your opponent's hand & you gain 6 VP. Lather, rinse, repeat.
Remember though, all of these pins have one turn of vulnerability where if the victim plays a masq, they have to trade over a high value card for whatever garbage the victim sends. Something like double tactician/masq can keep the pin from working indefinitely. Likewise goons or some other hand reducer can hit and delay the combo indefinitely (a strong scrying pool deck can hose these pins). Quite arguably a deck of NV/Bridge/TR is more powerful as it does not require an "attack" that can disrupt the combo so easily.
