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Heard this trick the other day on Podhammer - didn't know if it was general knowledge or not.
Trick: Park a Warboss on a Wyvern behind a hill the turn before you intend to Waaagh! On your opponents turn he should be well protected vs charges/shooting/LOS magic and on your turn when you declare the Waaagh! he will move at least 1" popping him up onto the hill where he now has LOS to charge anything he wants.
Two's to kill. Ahh, sweet sweet music.
First turn charge from wyvern is pretty commonly known.
It still relies on a decent amount of luck, with getting to go 2nd, having the right terrain in the right place, rolling well on the d6 movement..... etc etc