There has to have been something along the line of change which caused a new life form.
Sure. I have no problem with that. Abiogenesis has not been answered. More and more points to a natural beginning, but I'm being honest here and can say that whichever way biogenesis goes, natural or supernatural, I know that biological evolution is not wrong.
Nobody is saying a single mutation made something new.
He did. He said, "Can you give a modern example of a mutation that resulted in a different life form". When someones says "a mutation", they mean a single mutation. Otherwise it would have been plural.
Nobody is saying a hundred mutations are able to produce anything new, but something new eventually appears. Explain the eventually, please.
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I changed one digit at a time until I had a number that is twice as big as the original. One change at a time results in a series of changes to a complete bigger change, just like in calculus. The sum of many small changes can be much larger than the original/starting digit/point. If you have studied integrals, you know this.
How is skyscraper built? A few floors at a time. Or a pyramid. Or a battleship. Small parts, over long time, produce something that wasn't there before. Small mutations are small parts, that all summed together produce something. Do a number of changes, and the final result is different than the original.