These subs are fine, but the rules state that all subs must retain their primary typing, so in this case, Mawile would have to be Steel/Normal and Sableye would have to be Dark in you were to make it monotype. The confusion probably came from me specifying that rule last slate which made it sound like a slate specific rule, so I get the confusion, but just change it up before voting opens and you'll be good
Type of the Gigantamax Form: A new addition to To The Gigantamax that isn't done for any Gigantamax form in the base game, added to make the mod more interesting and make it easier to give niches to non-Ubers Pokemon. All Gigantamax forms must retain the base Pokemon's primary type

Type of the gigantamax form: bug
G-Max move type: Bug/Steel
G-Max move name: G-Max I have no ideas
G-Max move description: If the target uses a Fire-type move this turn, it is prevented from executing and the target loses 1/4 of its maximum HP, rounded half up.
There's nothing wrong with the actual sub, just be sure to think of a name for the G-Max Move before voting starts. Also, I assume you meant to put Bug in the G-Max Move Type section and Bug/Steel in the Type of the Gigantamax form section, since they're reversed right now
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Subs
Pokemon: Zarude
Type of the Gigantamax Form: Dark/Grass
G-Max Move Name: G-Max Harvest
G-Max Move Type: Dark
G-Max Move Description: Heals the user by 50% of the damage dealt and heals the user's status conditions
Competitive Overview: G-Max Harvest allows Zarude to keep itself healthy while Dynamaxed, making it a viable choice to Dynamax even if it's weakened earlier in the battle. This also makes it much harder to revenge kill and this combined with Max Knuckle or Bulk Up to boost Attack and Max Airstream (Acrobatics) to boost speed, a healthy Zarude after 3 turns can becomes a nasty sweeper
Pokemon: Kyurem-Black
Type of the Gigantamax Form: Dragon/Ice
G-Max Move Name: G-Max Future Shock
G-Max Move Type: Ice
G-Max Move Description: 50% chance to paralyze the opponent
Competitive Overview: Kyurem-Black is the only Uber that is not on the Ubers Dynamax banlist that hasn't been subbed yet this slate, but it's also of the best if not the best Dynamaxer in the tier, so I couldn't go too crazy with the effect. An Ice-type move that paralyzes makes the most sense flavor wise, though I made it a 50% chance to keep it a bit in check, making it enticing enough to be preferable to setting Hail but not broken.
Pokemon: Decidueye
Type of the Gigantamax Form: Grass/Ghost
G-Max Move Name: G-Max Arrow Raid
G-Max Move Type: Ghost
G-Max Move Description: Hard coded to 160 BP and traps the opponent
Competitive Overview: G-Max Arrow Raid patches up Decidueye's pretty weak-by-Ubers-standard 107 Attack by giving it a great 160 BP STAB move to throw around after a Swords Dance while it naturally threatens the best Unaware user, Quagsire, thanks to its Grass STAB. This combined with Brave Bird to provide Max Airstream can enable a Decidueye sweep
Pokemon: Incineroar
Type of the Gigantamax Form: Fire
G-Max Move Name: G-Max Moonsault
G-Max Move Type: Dark
G-Max Move Description: Hard coded to 160 BP, sets the Encore effect on the opponent and the Lucky Chant effect on the user's team
Competitive Overview: Incineroar is all about utility from Knock Off, to Will-O-Wisp, to Parting Shot, to Intimidate, so a G-Max move that allows it to leave a dent in something while possibly shutting it down with an Encore, while adding some flavorful utility in Lucky Chant, which may come in handy against Urshifu
Subs will end later today