Ok, here is what I would do(with CK):
1. Go to Activator and duplicate MirelurkQueenGooPile01. This is in case you need to edit the goo pile nif file.
2. Go to Magic Effect and duplicate CritMirelurkQueenEffect. Edit the new form by removing the script FXScatterImpactEffectsOnDeath. This leaves some yellow splatter below/around the goo pile, mostly when surface is dirt. Edit the other script's properties and set the new goo pile, that you created in step 1. Don't touch anything else. Confirm changes.
3. Go to Spell and duplicate CritMirelurkQueen. Edit the new form. Replace the old effect with the new, created in step 2. Confirm changes.
4. Go to Magic Effect and duplicate CritAcidEffectEnch. Edit this form's script, by setting the new spell, created in step 3. Confirm changes.
5. Go to Magic Effect and duplicate DamageHealth. Edit the new form by adding: flag->FX Persist and Hit Shader->PoisonDamageFXS. This will give the super mutant the same hit shader as the one from the bloatfly poison attacks. With the flag, the shader will be active for the duration of the magic effect. Confirm changes.
6. Go to Potion and duplicate a syringe form. Edit the name and description to more appropriate. Then replace the existing effect/s with ones created in step 5 and step 4. For the health damage set something like magnitude 300 with duration of 5. For the crit acid effect set magnitude to 1 and duration to 5. For each of the effects add a condition: Subject.HasKeword (ActorTyepSuperMutant) == 1. Confirm changes.
7. Create a Constructible Object for the syringe. Or duplicate existing one, so you will have the recipe and workbench filters. Set whatever you want components for a crafting requirement. Confirm changes. After everything's done save the plugin.
If you think that the health damage is a lot, keep in mind that higher levels have tougher enemies. Lower the magnitude and you will need multiple syringes to kill a super mutant. This is a matter of a personal choice and finding the right balance. Leave the timings as they are. But in case you want to play around, keep them the same for both effects.