While there are definately less resource-intensive options, Pro Tools can be a great sound-design tool as well. It has a per-channel envelope editor (kind of like a guy holding the volume knob for you and turning it up and down on demand) and with some creative use of multiple tracks and volume editing, you could quickly fade between, say, samples you recorded at the zoo of an orangutang, and a funky bird, which you could combine into a powerful screech (the dinosaur whines from Jurassic Park were a combination of a dolpin and a sea otter).
While Pro Tools doesn't have the abundance of free effects for it that Cubase/Logic/other VST apps have, I do believe the free version comes with a basic delay (echo) unit, pitch-time stretching, and sound reversal. You can do a lot with those effects and some creative recording.
I can post some examples of sounds I've created with these methods, and an explanation of how they're done, if there's enough demand. There's no 'step by step' process for creating sound effects, but I can give people plenty of ideas to try...
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--You notice that you have been turned into a pile of ashes.