Challenge completed - 375 reps:

back
8+6+5+5 Pull-ups (with rubber band) (24)
12x3 back extensions (s1:5kg, s2:5kg, s3:10kg) (36)
12x3 lower back bar (?) (new exercise) (don't remember weight) (36)
3x12 one more exercise for this muscle group, but I can't remember which (0)

biceps
12x3 Bicep bar curl (36)
12x3 dumbbell hammer curls (36)
12x4 dumbbell curls (48)

core
12x3 proper Dead Bugs with a big ball
12+25x3 core superset (name tba) (111)
4 minutes in total, 4 planks, no breaks (48)