really love those designs! Very creative, thanks ^^

Heist - Unconditional evasion is a bit too strong. For comparison, that's the same evasion boost in abilities like Sand Veil (20% in Sandstorm). It would be neat to have the ability tied to stealing items from opponents, so something like "Contact moves may steal opponent's held items. While holding a stolen item, +20% evasion".
Miasma - Seems very situational, since it only keeps poison from being cured, and not any other status condition. From how it's worded (does not specific active pokemon only), it may block things like the Natural Cure and Aromatherapy, but those aren't the most impactful (and Aromatherapy got removed, so...). Maybe an additional effect that benefits Toxic stalling, like reducing the damage dealt by poisoned pokemon, or cutting/eliminating their healing.
Death Grip - That's like two (not-commonly-used) held items in one ability. There aren't too many binding moves, and the only two that match the Water/Ghost typing are Clamp and Whirlpool. Other binding moves that match thematically are Wrap, Bind, Infestation and Sand Tomb. Snap Trap too, but that's a signature move of G-Stunfisk. I don't think there are other abilities that interact with these moves, so this is at least a unique ability.