RS-8 2 Defender Only
This event revolves around chill/freeze on your ops, and a bunch of high DEF low RES enemies without much attack. Penance barely cares about her attack speed, easily tanks the mobs, and kills them all with arts damage. The only thing left is the boss, who is fairly strong. Because Harold gains +50 ASPD in phase 2, I can't permastall him with Mudrock anymore, and must kill him somewhat quickly.
The blizzard mechanic this stage turns off after 999s pass (specifically, ops deployed during the blizzard experience chill/freeze cycles for 999s. Units deployed after the blizzard ends, or stay on for more than 999s, do not experience the blizzard anymore). This lets me effectively DPS Harold with Mudrock in phase 2, which I can do temporarily because I can use Flints to bait his attack away from Mudrock every so often. I run out of flints quickly cause I need one every cycle, but I can deal enough damage to win anyways.
If you need to copy this for some reason you can use some unit to buff Mudrock's survivability and just bring actual DPS instead of waiting 999s.
Music: Arknights RS Boss Battle Theme
0:00 Opener
2:08 999s later....