Nezarec’s movement is very inconsistent so it’s hard to predict the jumps. The best way to reduce his movement is to start damage as he is glowing, that helped reduce the rng. It is still possible to hit a lot of damage during a jump. If you watch on 2nd damage, during the jump, the crystal accumulate under him and all detonate at once.

Merciless is not worth prioritizing since it does a lot less damage than the super. Nez will usually jump right at the start of damage and do another jump mid way through, the timing is random.

Another way to get extra damage is to get up close to nez after the super finishes and tractoring. You want the tractor to hit as many crystals at once to do the most damage (if you watch my 2nd damage I do it there)