Mr Fusion is the ultimate coalescence of pump and energy.
If you've taken pre-workout before, you will notice a bit of the tingling feeling caused from beta alanine. This is normal and likely the first thing you'll notice. You will also notice increased energy and alertness before much else.
During your workout you'll notice an increased pump (blood flow) in the muscle you're training. Set after set you'll notice you can keep pushing further than you would normally and aren't fatiguing as quickly. You'll be able to workout harder and longer than normal with less overall fatigue.