Suggestion:
1) Remove the alias between zygarde and the following tags - zygarde_50_form, zygarde_50, zygarde_50_forme
2) Alias zygarde_50_form and zygarde_50 to zygarde_50_forme
3) Implicate zygarde_50_forme to the overall zygarde tag

Reason:(for suggestion 1) the tag zygarde is more commonly used to tag any form of the pokemon (be it cell, core, 10%, 50%, or 100% form). As such, people who are searching specifically for the Zygarde 50% form (zygarde_50_forme) will find difficulty doing so since art of the other forms (which are often tagged with "zygarde") will also show up. Fixing the tag aliases and implications would help remedy this.

Suggestions 2 - 3 are just tidying up that would follow if suggestion 1 is accepted