Counter Tips

Up-B Zero-to-Death can be DI'd, although it is very precise. Byleth isn't very fast so try to predict or look out for their attacks and Grab/Shield

It's tough to approach Byleth. Try to wait for him to whiff an unsafe option on shield then use your fastest out of shield option.

When you're at 0% as DK you shouldn't get close to Byleth because he can do the Zero-to-Death. You can DI, but it is very precise. You should approach him a bit with Bair and maybe when he gets greedy