There are several varieties of Possession pinning of which I am aware in addition to the forge case you can:
1. Draw their entire deck and generate a dead card hand - e.g. Kc/Governor them up to whole deck in hand - then use top decking or discarding to generate a 5 card green hand (e.g. Vault away 6 green cards, play a cantrip, end turn).
2. Similar to #1 set them up with only VP & actions that trash VP (e.g. Rats & Vineyards) or dead action combos (e.g. Smithy x7).
3. Kc/Chap (a much more common scenario than Forge) - yeah you may not be able to give them no cards, but putting all their better than copper treasure & useful actions into the discard works well. Very few decks have more than 12 really useful cards, particularly if you are wise about things like leaving all the villages & no terminals. When Kc/Chap is out, most people will be very kind and trash all the coppers anyways. Drawing from Kc, Chap, Green, and the odd crappy action makes for terrible hands.
A few other esoteric pins:
Masq/Cutpurse/Really strong engine. Have a way to gain coppers and get five of them into hand (e.g. Beggar, +buy, Iw, Haggler, etc.) play: Masq (pass a copper) -> Cutpurse (they discard a copper) -> Masq (pass a copper) -> Cutpurse (they discard a copper), repeat. Yeah you need a REALLY good engine and plenty of +action, but the important thing is to make sure that you swap their entire hand for Coppers and then Cutpurse them out (you can leave one copper as long as Poor House isn't out). Fails against Moat, Lighthouse, and durations (maybe), but it is fiendishly hard to stop the setup and it steals points - not trashes them.
Kc/B-crat/Masq/Wt/Engine: Like above, you want to masq over an Estate, B-crat it to deck top, and repeat. Kill the Silver flood with Wt. You can quite playing Masq once he has a single zero card hand thanks to the pin. Neither Masq nor Wt are strictly speaking required - you can just keep pushing back estates until he is B-crat pinned (but that is vulnerable to draw & deck discarding) Kc/Scheme/B-crat can be good if your opponent (poorly) skips out on using Kc/Scheme. Other options, like Apprentice, can work to kill Silvers.
Kc/Gov(Cr)/Minion/Cutpur : Draw all of both your decks, Cutpur him FIVE or more times, have him draw one more card, play minion for 4 cards. Play minions for Draw until you you have Cutpur'ed him another 3 times.
Kc/Gov(Cr)/Minion/B-Crat/Silver trashing: Like above, just B-Crat him 5 times, draw & trash silvers, have him draw one, minion for 4 cards, end turn.
