This is a hard question: I’ve seen a lot of wildlife, especially in Australia and the Indian Subcontinent - but I don’t think I’ve seen anything really really unusual. Some memorable memories though:
7 leopards in one day in Yala National Park, Sri Lanka
Mother sloth bear with 2 cubs riding on its back in Chitwan National Park, Nepal
Numerous Hectors dolphins with calves in Littleton Harbour, New Zealand
Being charged by an Indian rhino in Chitwan NP, Nepal
A “turf war” between 2 groups of 20+ monkeys: proboscis monkeys vs silvered leaf monkeys (the silvered leaf monkeys drove the proboscis monkeys off), this was on a pier at a farm near Kota Kinabalu, Malaysian Borneo
Wild Platypus in the Werribee River inside Werribee Open Range Zoo, Melbourne Australia
Black bears catching salmon, Alaska, USA
My first tiger, Jim Corbett National Park, India
My first squirrel, Dresden, Germany: I was so excited and my German girlfriend looked at me and said “yes, it is a squirrel” in a very unimpressed manner…