Venusaurite in PokeIdle: Mega Venusaur's Stats and the Same Drop Gap
If you only needed the stat line, Mega Venusaur is 80/100/123/122/120/80. If you needed a boss name, I do not have one.
Why this page is not a copy of Charizardite
The job is different. Charizardite is a choice between a physical dragon and a special flyer. Venusaurite is a single bulky Grass mega with defense and special defense both over 120. You are not choosing X or Y. You are deciding whether the stone exists on your version at all.
Io's megas module names Venusaurite. Net applies Mega Venusaur permanently at level 100. World does not list the item. Bulbasaur's evolution into Venusaur is a separate question, answered on the Bulbasaur page, because that line levels up long before any mega.
I still will not invent a fragment count to look helpful. See Charizardite for the sister gap and the item hub for the other searched items.
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FAQ
What typing and stats?
Mega Venusaur's listed spread is 80 HP, 100 Attack, 123 Defense, 122 Special Attack, 120 Special Defense, and 80 Speed.
Does net use the stone?
No. Net megas at level 100 with no item.
Does World have it?
No Mega Stone by this name in the World item catalog I checked.