ok 2 people are squaring off one with a void shield say at advanced the other guy slings a fireball at the shield and has to do the willpower check.

here is my question is this an opposed check

the way I take the rules he has to make a check and roll under 16 this doesn't make sense please someone explain this to me I'm confused.

This is probably one of the few times where just one d10 is used. In this instance it is a characteristic test using either WP or POW. In this particular instance, the attacker would need to roll lower (lower im assuming that this is showing control than just raw ability) than a 16 on their 1d10+POW/WP. The 16 comes from the difficulty the spell has set in place Intermediate difficulty being 16.

Void Shield
Level: 24 Action: Passive
Effect: Creates a barrier that absorbs and converts to nothingness.
In addition to a conventional shield, any supernatural power will stop
automatically, canceled if the attacker fails to overcome a WP or POW control test against the difficulty determined by the level of the spell(1d10 + WP or POW).
That is, if an opponent launches a offensive power against a magician who is protected behind a Void Shield at intermediate grade, and the caster obtains a successful defense, the attacker must overcome a WP or POW control check of 16 or attack will be canceled without
even damaging the shield. Similarly, any physical object stopped by the shield must pass a PhR test or be destroyed immediately.
Zeon Base(50), Intermediate(90), Advanced(120), Arcane(150)
Int R. Base(6), Intermediate(9), Advanced(12), Arcane(15)
Base: 200 Points of Resistance / Hard 14 / PhR 100.
Intermediate: 300 Points of Resistance / Hard 16 / PhR 120. <--------------------------- difficulty used-----------
Advanced: 400 Points of Resistance / Hard 18 / PhR 140.
Arcane: 500 Points of Resistance / Hard 20 / PhR 160.
Maintenance: 5 / 20 / 25 / 30
Spell Type: Shield

Now I myself cannot find it specifically but Im pretty sure that you add the stat and not the modifier it gives. If the modifier was added then most likely, the attacker would almost always previel easily with just a couple of spells, the shield would be nearly useless to have. Being that stat it would be harder and in my opinion be more defensive as it should be making the shield strong.

If I am wrong someone please correct me. If anything this should be of help and hope i explained well.

Arcana Exxet spells use the Core Exxet Attribute Check test, meaning you roll 1d10+add your Attribute for the value, it is no longer a roll under check.

The roll was changed? Which book was it in? Im reading the core/main book and it is showing as lower.

that is why i said Arcana Exxet uses Core Exxet(most recent core edition, unreleased in english/french) rules for Attribute checks.

Ah if that is the case I do not have the unreleased version. Why use one not translated yet? Seems like a hassle and could cause problems with other players who would be unable to check things if you ask me. (This may be for another topic discussion lol)