If you have LaDD on the field, and you play a card such as Shrink, does LaDD's effect activate immediately, or is your opponent allowed to respond with cards such as Magic Drain or Dark Bribe? How about cards such as their own Shrink?

In other words, if you activate a card that would cause your own LaDD to activate, does your opponent still retain priority to activate their own cards BEFORE LaDD's effect activates, or does LaDD force its effect onto the chain immediately? If so, would LaDD attempt to negate the newest chain link, or the original one that you played?

I think mandatory effects trump priority.

For example, if you have Stumbling and I summon Exiled Force, stumbling triggers automatically, even though I have priority.

Ah, I see. Thanks for clearing that up.

yep, what Zaq says. Unless they are simultaneous effects, nothing will get between chain link 1 and LADD.