I fight a D3 mainer on a semi-regular basis, and a few others at tournies. D3 might be Lucario's worst matchup. If it's not his worst, it's definitely his most frustrating.
-Luc is pretty much forced to approach for the majority, of not all of this match.
- Lucario can't pressure with auraspheres (AS) very well, partially because the waddles block it, but also because a surprise gordo can destroy Luc, making it too risky.
- D3 can obviously chaingrab Luc across the stage and set him up for some edgeguarding pain. I honestly don't see many gimps, but racking the damage on hurts.
- If Luc is lucky enough to get a forcepalm grab (FPG) on D3 when they're at low percents, he can take good advantage of it. It's rare though, and with D3's monster grab range it's often not worth the risk, unless D3 does something punishable.
- On the ground, D3's ftilt outranges everything in Luc's arsenal other than an AS. If close enough and timed just right, I suppose Luc could powershield it and punish, but I'm not sure about that.
- In the air, D3's dair, uair, and bair win over mostly anything Luc can throw at him. Luc can approach from the front (if D3 doesn't have enough time to turn around and bair), or a 45 degree angle to get in some fairs.
- If D3 isn't careful, Luc can charge an AS on top of his shield to chip away at it. Luc can mixup approaches coming out of shfair. The only unpunishable approach is shfair then jump away. If Luc can read D3 well enough, he can mixup beween shfair->bair from the other side, shfair->dair (delayed),shfair->nair, shfair->AS. All of those except for shfair->AS can be punished easily if D3 just holds his shield up. The trick is to make D3 think you're not using a 2nd attack, or that he has time to interrupt, then surprise him with a hit.
- The main problem is that any trick Luc tries obviously has a risk. If he outsmarts, D3 Luc stands to gain a short combo assuming D3 can DI properly, while if D3 reacts properly he gains a changrab across the stage followed by offstage fighting in his advantage.
- Luc wants to get D3 in the air and generally above him in this match, it's hard to do but a definite advantage.
- If D3 is forced to use his upB and land on stage, Luc can Usmash through it, or shAD then dair. If D3 is careless and hangs onto the edge too long, Luc can fsmash him. Luc can put some reasonable pressure on D3 recovering... as long as he doesn't fall for D3's neutralB.
- It's not uncommon for Luc to live to 140%, because while D3 can rack up damage, he doesn't have that many KO moves that Luc easily falls for or can't handle.
- Luc, however, has an even harder time KOing D3. If Luc is high in damage, then D3 still needs to be well into the 100's. If Luc is on a fresh stock, it's pretty easy for D3 to live to 170%.
If I had to slap a number of it, I'd say that at the very best it's 60:40 in D3s favor. I wouldn't hesitate to say 65:35.
Lucario's FTilt, Dair, and Nair will help greatly in this match.
I have to disagree with you there. D3 loooooooooves when Lucario dairs, because as long as he shields it (unless Luc is higher than he'd be from shorthopping) he gets a free grab. Ftilt can be decent, but the range of D3's ftilt makes it hard to get in such a position. Nair is great for finishing combos, but if you use it on a grounded D3 and didn't hit him with a fair leading to the nair, or manage to fake him out, you will get grabbed before you even land.