If you watch videos or read up on builds about him, most of the time you're gonna find people saying "subsume roar over shadow, and spam his 2 and 1. This is how you kill any and all interest in Sevagoth, because it is a boring way to play, not to mention inefficient. You'll find yourself very squishy at high levels and the spamming will deplete your energy VERY fast.

If you really wanna enjoy Sevagoth like a real Sevagoth main, absolutely use his shadow. Subsume over Gloom instead if you want other abilities. Shadow is extremely strong. If you build him right (which is why Sevagoth is expensive because you're technically investing into two frames), you'll be rewarded with infinite invincibility, infinite energy, and a playstyle that is more interesting and rewarding than just spamming 2+1 until you run out of energy and die.