Mat Block is only good for doubles/ triples. In singles, it's much better to use Protect considering Mat Block doesn't block status moves and will only work on Greninja's first turn in the field. Additionally, it has no increased priority like Protect. It'll also trigger Protean and turn Greninja into a Fighting type, which imo can be a bit useless and maybe a draw back if you're facing a flying type like Talonflame. Then again, Greninja has better things to do, like attacking. In singles, it's best not to use a move like Mat Block and just go on the offensive with Greninja.
As for a doubles set, there's not really any other supporting moves that Greninja can utilise in doubles. Spikes is really only for single battles, considering that switching is so much less common in doubles. I guess you'd just have to go full out offensive + Mat Block.
Greninja @ Expert Belt
Ability: Protean/ Torrent
EVs: 252 Sp. Atk, 252 Speed, 4 Atk/ HP
Nature: Naive/ Timid
-Mat Block
-Hydro Pump
-Dark Pulse
-U-Turn/ Extrasensory
Though, Mat Block is best on a bulkier Pokemon, really.
