25i-NBOMe is a drug similar in effect to LSD, but with a somewhat worse track record for safety. It's not likely to harm you, and unless you're fairly familiar with LSD, you might not notice the difference, but it has caused deaths due to severe vasoconstriction, which hasn't happened with LSD, even though many more people have used the latter. It's requires larger doses than LSD does, but it's still active at doses well under a milligram, and is usually sold on blotter paper just like LSD is.
Strychnine is also active in the LSD dose range. There was definitely some propaganda about strychnine-tainted LSD in the 70s, so it's hard to know if this has ever happened, or if it's just urban legend. But it's chemically plausible.
Fortunately, you don't have to just pray that your blotter doesn't have fentanyl in it. You can buy chemical test kits on the clear market and rule out all the culprits that should be cause for concern, and test that your blotter contains LSD (or at least a compound containing an indole group...). See https://www.reddit.com/r/ReagentTesting/ for links to vendors and more information.