There are very few exercises that challenge your core muscles and improve your stability as well as the L-Sit. This is how you do it
Trainer's Favourite Core Stability Exercises
How to Wall Sit: Techniques, Benefits, Variations
L-Sit Progression: 6 Steps To A Rock Solid Core
How to the L-sit hold to build a stronger core
Strengthen your core, improve your stability with the L-Sit
13 Exercises to Improve Your Balance at Any Age
Floor L-sit Progression Tutorial by Antranik
From ZERO to L-SIT in 8 Steps L-Sit Exercises and Progression At Home
How To L-SIT (3 STEPS) For Beginners - Core Strength & Progressions
L Sit Progression + 10 Steps To Improve - K Squared Fitness
20 Best Core Workouts For Women - Core Exercises For Stronger Abs
How to Do an L-Sit (and Why You Should)
L-sit Progression Plan - PHD
Give Planks a Rest. Try the L-Sit for Core Strength and Stability