1. Dragon Flags - full or ankle weighted
  2. Hanging Leg Raises - strict, straight legs toes to bar, sometimes ankle weighted
  3. Hanging window wipers - 180 deg Sweep with straight legs, 270 deg sweep for beast mode.
  4. Landmine 180 - essential to do properly to isolate the ext obliques. stand with both feet perpendicular to bar, heels must remain planted and dont lift or rotate them, torso must not twist or rotate at end of ROM, try to keep arms mostly straight, 20 reps with full ROM with climbimg weights per set but go light, it’s intense and will burn the obliques i.e. DOMS.
  5. Single arm farmer’s walk (50lbs) - Stand all, chest out, no leaning, don’t let DB or KB touch your side. I walk 10x150ft (45m). Great forearm/grip and to isolate the obliques.
  6. hollow body holds - hands straight behind head, 60 secs work, 60 secs rest for 5+ rounds
  7. hollow body rocks - 30 secs work, 30 secs rest for 10 mins.
  8. inverted sit-ups - use caution but hang from monkey bars and do it with a pad and safely - isolates abs … BW for starters, and I scale up to 10 and 25lbs plates held to my chest but this is intense and tends to work the back at higher weights.
  9. seated leg raises - straight legs, 10-15 reps per set - great for upper abs and compression,
  10. Seated leg lifts - straight legs and toes pointed - lift to 30-45 deg with hands next to or past your knees and hold for 10-15 secs repeat over and over. Great for upper abs and compression work.

Source

https://amp.reddit.com/r/bodyweightfitness/comments/9resw3/what_are_the_best_most_effective_core_workout/