This one is a bit hard to have but it’s a fun comp if available, specially against Sabers using the bond CEs (or nearly as much against Riders with other CEs).
In general I use it in Saber nodes and mid-difficulty Saber fights. Also a sometimes in harder CQ/Story level fights depending on the nature of the encounter. I EXplained it a few times before but pretty much what’s fun/cool about it is the Star manipulation: 3 20-Star bombs, 2 Star weight shifting skills, 1 big Star-gem buff (anti-Saber) skill, 1 Crit up Skill/1 crit passive. The set up is the most best against Sabers by far (by theme too), then Riders. But it’s pretty solid/refreshing in general.
Been using it for the Himeji Saber nodes recently. It’s great.
Note: Alter runs the chance of being ‘Crit out’, but since she’s got a big HP pool anyway and an (spread out) 7.5HP heal on low-cooldown she can sustain herself quite well, sometimes better that avg, in most scenarios.