If Pyke, Returned with Backline gets targeted by Block, which assigns him Tank as well, does he have Tank or Backline, and when should he be targeted?

The attacker (opponent assigning damage) chooses whether to treat Pyke as first or last.

Pyke, Returned naturally has Backline (must be assigned damage last). Giving him Tank via Block creates an exclusionary conflict — he can't be both first and last. Per Rule 460.2.c.7 (and FAQs 11355, 7737), the player assigning combat damage picks one of the two keywords to apply when assigning damage to Pyke. They can choose to treat him as Tank (damage him before other non-Tank defenders) or Backline (damage him after other non-Backline defenders), but not both.