MDFC creatures act strangely when entering off Arthur, Marigold Knight Trigger

[Edasiba]

Whenever a creature that happens to be an mdfc enters the battlefield from Arthur's attack trigger it will enter tapped but not attacking. In addition, it will stay on the battlefield despite Arthur's end-of-combat trigger trying to return it to hand. The weirdest thing is that the creature will be invulnerable to damage or destruction. Example creatures are [[Glasspool Mimic]] , [[Witch Enchanter]] , and [[Pinnacle Monk]]

[z33kz33k]

[[Arthur, Marigold Knight]]

[github-actions]

Arthur, Marigold Knight - (Gatherer) (Scryfall) (EDHREC)

{2}{U}{R}{W}
Legendary Creature — Mouse Knight
4/5
Haste
Whenever Arthur and at least one other creature attack, look at the top six cards of your library. You may put a creature card from among them onto the battlefield tapped and attacking. Put the rest on the bottom of your library in a random order. Return that creature to its owner's hand at end of combat.