Leona vs Lulu: baiting Whimsy before you commit
The engage does not fail because of damage. It fails because the polymorph is up. Bait it first, then the lane is normal again.
Step to the edge of your engage range and hold. A cautious Lulu will use the buff defensively on her ADC or the slow on you. Either one opens the actual window.
Once the polymorph is spent you have a fixed number of seconds, not the rest of the wave. Commit immediately or reset the bait; hesitating gives the cooldown back for free.
Then the lane is not the win condition and forcing it is how supports lose games they were not losing. Rotate, take vision, and let a different lane decide.
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