Rayman Legends isn't particularly hard, but require you to get a predetermined amount of points in the daily challenge levels, which if you only get gold trophies in them, should still take like 3 months.
The Vita plat for Legends is actually harder - because they changed a couple of trophies round and require you to get a diamond rank once as a separate trophy. As you can imagine, since only the top... 1%? get a diamond rank that's hard enough when the game was new let alone where it is now with just a tiny fraction playing. Thankfully Legends is one of the few games I can actually claim to being good at, so I've managed to plat it (alongside the PS3 and PS4 releases, because its an amazing game) but yeah if your not so great at it then the list is pretty damn long/hard for sure.
Crash Bandicoot 4 is the most recent game that sprung to mind for me seeing as the NSane relics are pretty tricky to get (especially on certain levels) not to mention the plat time trial relics. I'm only a good 35% of the way to the full 106% completion and I can already tell some of these levels are gonna been pains in the ass to perfect. Amazing game though!
A couple of smaller/retro style games that put up a fight for the plat/100% are:
Super Meat Boy (already mentioned above)
Cursed Castilla/Matilda Castilla - its basically an easier Ghouls n Ghosts BUT has one particular trophy that elevates it above pretty much anything GnG asks you to do (unless your mad enough to try a flaming torch only run) - namely finishing the game with your flaming sword. Now that sword is a badass weapon, its strong, great range etc. so really if you had to clear the game with any weapon, that's the one to use. The catch? You can only get it at one single point in the game, early on at the beginning of stage 4 I believe... and if you die, its gone. And while you can keep a save file at the beginning of stage 4 to easily restart your run, it still means you gotta do stages 4, 5, 6, 7 and the secret 8th stage in that single life - and even though its an "easier" GnG that's really not saying much. I've managed it once, and never managed to replicate my success with the separate Vita plat...
Mega Man 10 - not a plat, or even a gold trophy because Capcom clearly hates me, but unlike MM9 which gives you an optional objective to finish the game without taking any damage, MM10 takes that "Mr Perfect" challenge and slaps it into the main trophy list. Now its not all bad news, you can save between levels and play on Easy mode, but you still gotta learn every level inside out, including the penultimate Wily Stage which has you fight 11 bosses back to back (8 robot master refights, 3 phase Wily boss fight).
Volgarr the Viking - This is a retro game that throws back to stuff like Rastan. The main game itself is far from a pushover what with incredibly limited checkpoints and some hard to see coming obstacles. So beating the game once feels like an achievement in itself, but getting the best ending and beating the secret level demands more from you - mainly that you need to hit almost every chest you can find, take essentially no damage as you do this (as you need warrior spirits to get to the alternate levels, which are only acquired if you hang onto the flaming sword) and you also cannot continue. Its also strongly advised to never die either since that makes getting more warrior spirits harder. So essentially you need to learn the game back to front and play an almost perfect game - while you can die, you can only do so a very limited number of times and you really dont want to until you reach the last stage, as that's hard enough as it is.
