If you ever find and want to fight a alpha rex here’s 3 steps that help a lot

1. Lead it to a large body of water (note check for jellyfish before doing this)

2. Spray it down with wyverns until it starts to get bloody (note watch you stamina and also make sure that you don’t get hit and lead it out of water)

3. Find a hill too with a flat rock and spray it down (note when they retreat let it because it might be glitched trying to eat and dead carcass)

Also note that blood wyverns are the best for killing these!