If I have multiple Regieleki VMAX with the "Transistor" Ability in play, will my Basic 
Pokemon's attacks do +30 more damage for each one?
Yes, the Transistor Ability will stack.
Transistor
Other known variants
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Regieleki VMAX
- Type
- POKEMON
- HP
- 310
- Energy Type
- Stage
- VMAX
- Retreat Cost
- Weakness
x2- Regulation Mark
- F
- Rarity
- RARE HOLO VMAX
- Illustrator
- N-DESIGN Inc.
- Set
- Silver Tempest (SIT)
- Number
- 58/195
Abilities
Transistor
Your Basic Pokémon's attacks do 30 more damage to your opponent's Active Pokémon (before applying Weakness and Resistance).
Attacks
Max Thunder and LightningDuring your next turn, this Pokémon can't attack.