Adaptation Distillation: "The Spring Snow Incident" is a short episode compared to the game, so the battles are shortened and some events are truncated.
Armor-Piercing Question: Sakuya asks Reimu, "I wonder, if someone dies in the Netherworld, will she rest in peace?", leaving Reimu to consider if she would leave Marisa at Yuyuko's mercy because of her laziness.
Call-Forward: Marisa's complaint about hearing youkai underestimating humans again refers to Patchouli's similar comment in the next episode.
Demoted to Extra: The anime usually has all the playable characters be involved in the incident, but here Sakuya simply shows up and makes Reimu do her job, rather than be involved directly.
Early-Installment Weirdness: The end credits for this episode display a motion comic with Super-Deformed versions of the cast when all later episodes (except episode 7) have their end credits display black-and-white artwork of stylized versions of characters relevant to the episode.
Graceful Loser: Yuyuko, just before Reimu defeats her with Fantasy Seal.
Gravity Screw: Marisa flies upward through the portal into the Netherworld, then hits what seems to be a ceiling until her POV inverts and she finds herself lying on the ground at the foot of the ridiculously long staircase.
What the Hell, Hero?: Sakuya gives a very mild version to Reimu for not going out to deal with the incident.
Xanatos Gambit: Even though Yuyuko's plan to make the Saigyou Ayakashi blossom failed, at least it provided a distraction to allow Sanae to enter Gensokyo.