Pony Fantasy VI Remake

No, the Mammoth cannot one-hit kill Snips and Snails. It only uses Blizzard if you're above level 5, which you will not be when you fight them.

The ProtoTroop is weak to whatever element is opposite he is using; when he uses fire attacks, cast ice, if he uses poison, hit with holy. Scan can help you recognize those patterns if they're unclear. If you don't have the element he's weak to, hit him with another magic attack to provoke a WallChange to something to you can work with. Alternatively he only has 777 MP, so you can Runic and Rasp to outlast him and disable most of his offense. You just didn't fight him right.