Use ready/instant fusion to summon Allvain and make Lvl 10 Synchro monsters.
ChengYing synergises so well with Eater, Orochi (that we have as a 4 of with foolish burial)... It s kinda crazy.
Super poly can be played in this deck, but you'll have to save extra deck space for it.
Kaijus are playable but you miss space. That's why I used Lava Golem. Ra Sphere mode does not work here because it needs to be normal summoned and clashed to much with the castle.
Another idea is to use mind control to get back lava golem (it's level 8) or any monster from the opponent that could be treated as lvl 8 for XYZ summon the new Vampire xyz monster...
The side is mainly going first cards, which you'll need if you win the first game going second.
A lot of option for a great and modern Gren Maju Deck!!