Given that the Federal Reserve wants unemployment numbers to rise, they're specifically trying to make share capital worth less, and borrowing capabilities cost more, making revenue-poor corporations stop being so optimistic. so I would just expect lower valuations with much lower revenue multiples (or price to equity ratios), for that reason alone.
Slowed growth in China is always a threat because thats a key revenue driver for many large western companies. Then sure, there is the leverage and accountability problem with Chinese real estate, but I don't get the impression that contagion is that big because nobody thinks that is a safe bet and also avoid too much exposure to the domestic chinese lenders involved. The rumors behind Tether just aren't big enough to matter for this, could only be a slight sting to the commercial paper market and a moderate "finally" for the crypto market as a tether implosion would probably increase confidence there after steep selloffs.
Oil/gas volatility is probably going to have some casualties.