I'm adding 200 instead of 100 to the stats because Smeargle's BST is utter crap 250 and even adding 200 the result is mediocre.
Mega Smeargle X
The idea of having all moves of the game fascinated me, and I found absurd to have access to all those powerful attacks (Steam Eruption, Blue Flare, Bolt Strike, V-Create, Dragon Ascent...) and not have the power to use them, so here we have the all out attacker Smeargle, with decent offensive power backed up by Protean to get STAB in all moves and a good speed tier. On the other hand, absolutely every priority in the game is likely to OHKO it, so this balanced things quite a lot.
Mega Smeargle Y
And here we have the ultimate tank, with access to every utility move ever and Prankster because why not? This thing is actually bulkier than M-Sableye, although it lacks its immunities and resistances. It has access to Spore, Will-o-Wisp, Sticky Web, Recover, Rapid Spin, Heal Bell... Whatever you need in your team, this guy has it, backed up by the bulk to make good use of it. However, with a mediocre defensive typing and no offensive power at all, it's very likely to suffer from the 4 moveslot syndrome and be setup fodder for sweepers once a sleep bait has absorbed Spore and the sleep clause is active. It also suffers from Toxic, as it can't bouce it back as Sableye does.