I definitely think the developers should not ignore recently added moves (especially daring and determined strike) when making changes to older creatures. It allows one move change to make a drastic difference.
That’s a really good idea for stygidaryx to have lethal rampage and run for two reasons. One it needs a buff. Two it’s legendary ingredient has a defense shattering impact, and when you make Stygidaryx it no longer has it.
I like lethal Rampage and Run on it, but the one problem I think is the delay. It’s too long! Your only damaging move that doesn’t swap you out is RS, so you’ll be doing minimal damage until turn 3 when you can FINALLY use this move.