Episode 3: Reinhard completely destroying Elsa with a sword he picked up from the ground. Special points for the animation during his sword swing.
Arc 2 Season 1 Episodes 4-11
Episode 10: Subaru goes out to rescue Rem after she puts herself on the line to save him, despite the fact that he's cursed. He ends up fighting a horde of Mabeasts with Ram that he lured using the side effects of explaining Return By Death.
Episode 15: Rem puts everything on the line to save Subaru after he was kidnapped, having her limbs and neck broken and left for dead. She heals up enough just to inch closer to him and break him free of his chains.
Episode 19: Taking all the lessons he's learned, Subaru successfully negotiates to deal with the White Whale and personally leads the charge.
Episode 20: Willheim shows why he's known as the Sword Demon by hacking apart the White Whale like butter.
Episode 21: Subaru jumps onto the White Whale's horn after being launched by Rem's ice attack. He proceeds to taunt the White Whale while doing a Badass Arm-Fold and then jumps off, tricking it into a trap.
Episode 24: After all the trouble that Petelgeuse caused for Subaru, it's incredibly satisfying to see Subaru mock Petelgeuse with one simple statement: The fact that Subaru bears the miasma of the Witch of Envy means that he technically has more favor with Satella than Petelgeuse does. Subaru even makes light of Return by Death, stating that he's so much closer to Satella that she's literally grabbed his heart. Subaru also rejects the title of Archbishop of Pride (even though he technically qualifies for it) because he simply wishes to be Emilia's knight.
Arc 4 Season 2 Episodes 1-8
Episode 6: The big fight scene pits Ram against Elsa, who's already well established how dangerous she is. After a whole season of being overshadowed by Rem, it's rather impressive to see Ram take swift command of the situation, repeatedly come up with strategies to escape, and even land a significant attack that makes Elsa bleed.
The second season's first opening has plenty of awesome moments along with stunning imagery:
The OP starts with Echidna releasing a beautiful swarm of green butterflies that illuminate the new cast members.
We get the first hints of Subaru's backstory, as we see him trudge among dirty city buildings beneath a cloudy sky, before cutting to brief shots of his parents.