This is non canon so don't come at me for it it's only a suggestion
Since most of the 5th moves change all other previous moves (except water and thunder) how about serpent does the same thing.
When 5th move is used you get an animation where the user gets wrapped around by snakes and the snakes fuse in with him making him stronger.
First move would be an aoe of the poison gas that a snake spits out [block breaks]
And gives the effect of poison for 8 seconds. [20 cd]
Second move will consist of the user throwing 5 snakes in random directions that can be blocked but give poison effect or if hit would fling the player +blind the player for 7 seconds. [11 cd]
Third move will make the user ride a snake for a short distance if hit then the oppon ent's would be flung (kinda like spider dads 1st move). [10 cd]
Forth move would make it rain poison that can be blocked but leave a slight amount of poison effect. [10 cd]
Please leave any comments or changes you might think would be necessary or of some things seem too op.
🙂