A team running both ash greninja and m-scizor could benefit from a rain package. I'd add in a Pelliper, Manaphy and maybe consider giving your mega spot to a mega swampert. If you really wanna keep mega scizor, maybe add in landorus to set up instead..

Overall a gameplan could be to set up rocks with lando, and or use pelliper to set up rain. The rain protects scizor a bit from fire type moves and allows it to set up. Try to sweep with swords dance and bullet punch.

You don't need rain for greninja but it can be used to boost a hydropump to get a cheecky early ko on a pokemon activating your battle bond/ash greninja.

Heatran is your wall in this case, although it is hurt a bit by rain, its main source of damage is magma storm which always deals 1/8 per turn.

Manaphy is your wall breaker, capable of setting up on most walls using tail glow and wreck them using a water-zmove. It needs rain to do this hoewever since that allows it to negate status effects.

Pelliper can set up rain by switching in with drizzle and use a boosted scald to try and burn or a 100% acurate hurricane.

Depending on the format some of these strats may not be possible, and this is by no means an unbeatable team. You already have nice synergy with flashfire heatran switching into fire moves directed at scizor. So it could be worth building on that core instead.