
In-game, spasm looks like just a generic cripple in the description window. On web tools it shows -40% melee vulnerability (which I believe to be the intended effect?) The actual effect applied not only effects melee vulnerability but also non-melee (spell damage.)
Overbearing Power also looks like a generic cripple debuff in the spell description window. Web tools show it as -30% spell vulnerability, with other cripple stats (-AC, str, etc). Though this does properly only effect spell damage (max hit with melee does not change after this debuff is applied.)
Example: Target is debuffed with Entwining thoughts strike (proc off enc nuke that debuffs resists, overwrites wrath of phantasmist IV) and enc 2.0 resist debuff (phantasmists secret). With just those two, her nuke crits for 33k. Add Overbearing Power Rk. III, the nuke crits for 40k. Add Euphoric Spasm Rk. III (melee debuff), the nuke crits for 57k.
(edit: these are all with rk. III. Not sure if the same things display with rk 1 and 2)