If Yasuo Remorseful attacks a battlefield and you have a tank, can he bypass it?
Yes, Yasuo, Remorseful can bypass a unit with the Tank keyword when using his "When I attack" ability.
The Tank keyword is a passive ability that specifically restricts how combat damage is assigned during the Combat Damage Step of a showdown. According to Rule 741.1.b, Tank is functionally short for: "I must be assigned lethal damage before any other unit with the same controller as me that does not have [Tank] during combat resolution."
Because Yasuo's "When I attack" ability is a triggered ability that deals damage outside of the combat damage assignment process, the restrictions imposed by the Tank keyword do not apply to it.
Summary of the interaction:
- Tank only restricts the assignment of combat damage during the Combat Damage Step (Rule 443.1).
- Yasuo's ability deals damage as a triggered ability when he attacks.
- Since Yasuo's ability is not combat damage, you are free to target any enemy unit on the battlefield, regardless of whether it has the Tank keyword.
Note: I could not fully verify this ruling against the retrieved rules.