Bonjour je voudrait savoir a quoi il sert c'est marqué quil ameliore les compétences pourtant sa change rien en jeu quand je l'équipe vous savez pourquoi ?

It boosts the stats of the character that's holding it in his bag. Only works in Infernal or Ultimate Difficulty. For each additional floor that you complete in the Labyrinth of Chaos, the seal will grant a more powerful boost up to 25% when the 99 floor of the Labyrinth or Chaos is completed. Its effect works on any stage, but does not stack with another seal in a bag. Completing floors in the Tower of Mirages does not increase the boost of the seal. At top level, these are the stats affected:
25% up attack
25% up defense
25% increase rate of critical (Applies to Elves)
25% reduces MP consumption (Applies to Sorceress and Wizard)
25% reduces Power Smash cool down (Applies to Amazon, Dwarf and Fighter)