Yes, you can stack annihilator triggers as long as you have added the annihilator ability to a creature that already has it, or multiple attackers with the ability
Funnily enough, while ETBs continue to drop in price, the booster box is actually on the rise, jumping from around $200 just last week to almost $230 now
On the stream, Zakeel Gordon, Executive Producer for the Final Fantasy set, noted that summons will appear at all rarities. This should mean splashy mythic rare summons, and also some nice complexity for Pauper
But honestly, all one can do is speculate at this point
Call Energy not only provides Colorless Energy but lets you look through your deck and place two Basic Pokemon onto your Bench
So lets get into it, and calculate exactly our odds for opening certain packs, then compare those rates with chase cards from previous expansions