It's actually very dificult to level airstomp.
Before I rebooted, I only earned level III it in level 45... But I spent much time not using it.
If you wan't to level it quickly (and note that "quickly" is just an expression) you have to use it every time you can.
The best map I've found for Airstomp is Evac Zone (you have a great visibility over the ground from the building tops - once I had 8 kills by airstomp in one game in this map -), Skyline and City Hall.
Keep trying (you will die a lot xD) and remeber to jump to the position that your enemy will ocupy in 2/3 seconds (it takes time to perform an airstomp). That is the most dificult aspect of airstomp. Also, only bother to jump from high positions (more than 4/5 meters from the ground). Otherwise, it is useless (you can land right next to an opponent, that you won't even make him flinch).
When you finally reach level III, it is amazing. You get up like 100x faster than with level I abd II.
Cumps,
omega4
PS - try to get an airstomp kill from the top of the lighthouse. It's unforgettable
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I know all the theory... but getting my Air stomps to work is a totally different story
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