Basic Union Monster support Spell Cards are useful, such as "Frontline Base" and "Roll Out!". If you choose to include such cards, "Heavy Mech Support Platform" and "Heavy Mech Support Armor" provide more targets, and are useful when equipped to the fusion monsters, as it protects them from being targeted or destroyed by your opponent's cards. You can also equip the fusions with "A-Assault Core", "B-Buster Drake", and "C-Crush Wyvern", summoned to the field at once via "Union Scramble", and you will have a powerful monster that cannot be targeted by (if it is equipped with "Heavy Mech Support Armor") and is unaffected by all your opponent's Spells, Traps, and monster effects (if equipped with all three "ABC" union monsters). If they are all equipped to "A-to-Z-Dragon Buster Cannon", it is likely to keep a lot of pressure on your opponent during a duel since "A-to-Z" is a 4k beatstick that they will not be able to target with the likes of "Castel, the Skyblaster Musketeer" or "Dark Rebellion Xyz Dragon", nor have their spells, traps, or effect monsters' abilities work against it, that also has the ability to negate anything they attempt as long as its user has cards they are willing to discard.
LIGHT-support spells in general also work, particularly "Honest", seeing as it is both handy to protect the individual Union and Normal Monsters in addition to being a spectacularly effective way of paving a way to victory for the bigger Fusion Monsters, especially "A-to-Z-Dragon Buster Cannon". A particularly devastating strategy is swarming the field with the base monsters, then using "Limiter Removal" to give them a huge rise in power just to finish the turn with fusing them together. "Dimension Explosion" can act as a sort of "De-Fusion" for these cards, only the targets to return to the field or Extra Deck are not limited to Fusion Monster-Fusion material relation. "Lightwave Tuning", "Torque Tune Gear", and "Chaos-End Master" are useful for any Synchro Summons.
Although "VWXYZ" has the ability to banish 1 card, the effect of "XYZ-Dragon Cannon" can be used multiple times in a single turn. Therefore, by removing "V-Tiger Jet" and "W-Wing Catapult" from your Deck and relying solely on "XYZ-Dragon Cannon" and "ABC-Dragon Buster", you are left with more room to fill your Deck with other useful cards. By using a similar method to the one explained above you can create a Deck that can Special Summon "XYZ" and has Fusion Monsters that aren't so tough to get on to the field. The ABC Union monsters and "Heavy Mech Support Armor" can be used to protect your Fusion Monsters, "Power Tool", or "Cyber Dragon" monsters from the negative effect of "Limiter Removal" without needing to worry about sacrificing Equip Spell Cards being used with "Power Tool Dragon".
Using cards like "Reckless Greed" (carefully) to draw cards to use as 'ammo' for the effect of "XYZ-Dragon Cannon" is an effective way to clear the opponent's field. It is also good to play an "Overload Fusion" and "Cyber Dragon" for a "Chimeratech Overdragon" to put out enough ATK to finish you opponent off, or as a back-up plan if your "A-to-Z" monsters are destroyed. By the time you have an "XYZ-Dragon Cannon" on the field and used its effect to destroy your opponent's cards you should have enough monsters in your Graveyard to use "Overload Fusion". Also, remember adding a few Synchro Monsters like "Karakuri Shogun mdl 00 "Burei"" and "Power Tool Dragon" (equipped with Double Tool C&D) to keep the opponent occupied until you can Summon an "XYZ-Dragon Cannon".