Saber: Theater of the Deranged allows her to attack the enemy even through any Guards, all the while weakening them and showing them the might of a Saber.
Archer: Unlimited Blade Works vastly increases the effectiveness of all projections, allowing our nameless hero to absolutely decimate the enemy with repeated use of Caladbolg or Triple-Linked Crane Wings.
Caster: Eightfold Blessing of Amaterasu removes her mana costs for one turn, allowing her to nuke down the enemy with her powerful spells.
Any time you block an enemy's Noble Phantasm with Rho Aias, particularly hearing the enemy's response.
The best moments were blocking Gae Bolg as a Continuity Nod and Gawain's Galatine, because his incredulous response is hilarious.
Blocking Gae Bolg was particularly satisfying because Luck is a Dump Stat, and the damage it does is based on luck, so it was either 'block it with Rho Aias' or 'get insta-killed'.
Isn't Luck the dump stat for all or most Archer players? After all, his E-Rank Luck is canon.
Monji Gatou pulled a Heroic Sacrifice by passing through Jinako's barrier, that would dissintergrate any trespassers from entering it, in order to obtain her SG for the Protagonist.
Shinji got himself killed by Meltlilith, in order for her to absorb his data due to his intelligence. But, what she didn't know that Shinji knew this would happen, that he infected himself with a Virus awhile ago. Once Meltlilith absorbs him, the virus would affect her, taking away her invincibility, giving the chance for the Protagonist to finally defeat her.
Archer being able to trace Excalibur in Unlimited Blade Works.
Should you have Gilgamesh and ask Andersen to evaluate him, Andersen will be calling out and roasting on Gilgamesh's flaws and story... and managed to be alive at the end of it! It takes guts to call the freaking King of Heroes out.