Hiver, if it's not too spoiler-y, what would the SI's main goal be while in WoW?
Is it to change the plot, for better or worse, and essentially be a role-player? Will he be more of a power gamer, whose aim is to learn magic and skills, and acquire loot and artifacts to make him stronger, with little regard in how WoW's story unfolds?
Both have advantages, but if the SI's strong enough, it might be fun to be a griefer instead: like staying in a fairly well important area and killing everyone who tries to do stuff there. Kinda like how some higher level players camp at places and kill the lower level ones to keep them from leveling up. Except it's not a game, so maybe the aim would be to keep some people from meeting certain objectives.
Or pulling of the equivalent of an Leeroy Jenkins, by provoking some large undead or demon armies in an epic agro. Let them chase you to the point where the stronger characters like Thrall, Jaina, and others would have no choice but to deal with them.
As for summons, forget subtle! Go for multiple infernal summons dropping from the sky like meteors, just like you see in the RoC cutscene. So the summons would hit like a fireball or magma attack,
then rise from craters to follow your commands!