Ok say I have pyramid turtle in attack mode, and my opponent has a newdoria. also in attack mode. I slam turtle into newdoria. Both hit the graveyard because they are of equal attack. And both activate their effects when they hit the graveyard. So my question is. Can my opponent use newdorias effect on my special summoned monster that I got with turtle?

I guess the chain would be: First on activation, the pyramid turtle (turn player goes first), then newdoria chains, so, it resolves first newdoria, destroying some monster on the field, and then pyramid turtle resolves summoning your monster.

Hope this helps.

They are both sent to the Graveyard at the same time. Since you are the turn player, your turtle would be link one, and their Newdoria would be link two.

Link 1: Pyramid Turtle
Link 2: Newdoria - tries to select a target (no monster has been summoned by turtle, so it would have to select another monster on the field. If there is no other monster, no target can be selected)
- chain resolves
Link 2: Newdoria destroys target (if there was one)
Link 1: Pyramid Turtle summons a Zombie monster from the Deck

Even if it was the other way around, Newdoria couldn't destroy the newly summoned monster because it selects its target at activation, not resolution.

Oh thank you oh wise 1 from the heavens!!!!!.........