from UDE's Judge Certification Program (YGO)
Q:
When I Special Summon "Lava Golem" onto my opponent's side of the field by Tributing 2 of their monsters, do I have priority to activate an Ignition Effect?
A:
When the Turn Player successfully Special Summons "Lava Golem" onto their opponent's side of the field, they have priority and can activate the Ignition Effect of a monster they control or a Spell Speed 2 or higher effect.
http://entertainment.upperdeck.com/community/forums/thread/1574111.aspx
Q:
When I Special Summon "Lava Golem" onto my opponent's side of the field by Tributing 2 of their monsters, do I have priority to activate an Ignition Effect?
A:
When the Turn Player successfully Special Summons "Lava Golem" onto their opponent's side of the field, they have priority and can activate the Ignition Effect of a monster they control or a Spell Speed 2 or higher effect.
http://entertainment.upperdeck.com/community/forums/thread/1574111.aspx