I'm not talking about ISDA stuff. There are tons of OTC instruments out there that are also acessible by retail
For example warrants and certificates. stuff like this: https://www.euronext.com/en/for-investors/warrants-certificates These are big in the EU and most issuers have around 200k products to offer. OTC, local exchanges, Direct Dealer RFQ (when you're large enough), etc. They're all non fungible bilateral derivatives. Most of them are trash but some are mispriced. However, I trade what's hot at the moment. Used to do a lot of FX NDFs, too.
For example you could buy puts, sell calls (aka a risk reversal) and bet on the call touch. When the underlying gets there and you have a profit you can either close the position or fly it off with buying wings for the same vols you originally sold the calls for which gives you a nice bet on vega and wing vol. On the other hand it could just be a vertical that you flattened with regards to delta and turn it into a fly by purchasing wings. Or you just made a bet with two strikes in an illiquid chain. Most of the time it's easier to just buy or sell a single strike and turn the position into a fly opposed to just liquidate at the market. You could also be long stock, sell two call verticals against it and buy a put to make some dosh in a range without capping your upside. Synthetics are everything