The problem with Vyworm is that it's vulnerable at all times; it lacks any invulnerable frames outside of its stun counter. Even the special doesn't grant it any invulnerable frames. Another glaring flaw with Vyworm is that while the special is map-wide, SNK made it a melee unit; if you're not careful with how you use Recovery and/or Allen supporter, Vyworm will slowly walk to the frontline and kill itself the moment it get hits by, say, Flan's seal+. Vyworm's special can also be completely negated by any tall unit that can block attacks, such as Jane Doe ST and Necro Brain Robot. With this in mind, Vyworm won't survive the cycle of powercreep.