http://imgur.com/KLKGqrT XclizyX has three restricted pokemon (Groudon, Kyogre, Xerneas) when VGC 2016 limits every team to two of these mons. One thing to consider is maybe he is using an older version of PO, which I was unable to check because he left immediately afterwards.
tiers.xml does not show any errors within it, so the error is likely to be with a specific client. I have replicated it with Android client, continuing to test things out now. EDIT: This seems to happen due to the placement of the Pokémon. It allows me into the VGC 2016 tier with the tier replicated exactly as it is in the screenshot, with legends in any of the first 4 slots, and then 2 others in the final 2 slots. Moving the team about to have 3 legends in the first 4 Pokemon means I am not allowed to join the VGC 2016 tier. HOWEVER, it will not allow you to actually battle with 3 or 4 legendary Pokémon, and forces you to rearrange so that you are using a maximum of 2 at a time. EDIT2: THIS ISN'T JUST AN ANDROID BUG. I have done the exact same thing with the Windows client just now. It seems to check if the Pokémon you are actually going to use for the battle in that tier break any conditions for the tier in tiers.xml, but not any slots that would not be used. It checks again before you confirm your team in Team Preview, so that it prevents any illegal teams being allowed in the battle. This needs to be changed so that tiers.xml's conditions read all 6 slots, even if the battle will be restricted to less than 6 Pokemon for Pokémon that are legal in the tier. (18:48:55) fitzy: if you want to edit the post (18:49:10) fitzy: what you suggest would break vgc 10 (not like anyone plays it) (18:49:21) fitzy: You were allowed to bring 4 back then but use two (he's talking about legendaries) So either PO needs to get rid of the older VGC tiers, or we need to carefully look at how to fix this. I suggest the former tbh.