As for a few other possible ideas, I have a few.
The first is M Swampert EX Promo which does 160 for 2 water and 2 colorless if you mill the top 3 cards of both players decks. Maybe this could work paired with Palkia to set up Swampert without need for special energy, then just run a heavy count of recovery cards to shuffle energies/Pokemon back into the deck. The main pros to this card are that it isn't reliant on any special energy if Palkia and Max Elixir are used and can be powered up in one turn, not to mention that the milling effect will put a lot of pressure on the opponent, losing 3 cards per turn. But at the same time, there are much better milling strategies out there like Houndoom EX which does it for only 1 energy and only discards from your opponent with the only downside being that it only mills 2 instead of 3. On top of that, again you are stuck at that 160 damage output whereas you would much rather be dropping at least 180 to take knockouts. So maybe Palkia Swampert Mill could become a thing, but more than likely its just me trying to stretch an idea that really isn't meant to see the light of day. There's also the added benefit of regular Swampert EX's first attack, which could maybe work in a deck similar to the old SpeedQuaza by running nothing but water energies, Swampert, Palkia, and Max Elixir, to focus on powering up Swampert quickly and dealing heavy damage. But in that scenario, running Palkia becomes more of a hindrance than it does help, so maybe not a good partner for Palkia.
Another option may be M Blastoise EX, who can actually hit that nice 180 mark with his attack at the cost of discarding 2 water energies. Again, the list would center around using Palkia with Max Elixir to try to get 4 energies on Blastoise in one turn and then begin smashing. It would have to run a heavier count of recovery cards (mainly super rod to ensure the energy is in the deck to be accelerated with Palkia/Max Elixir), but it does hit a decent damage number. But it suffers from that same problem of having to run Manaphy to give free retreat due to Blastoise also being a fat retreater, and the regular Blastoise isn't particularly stellar, so I'm not entirely confident it would be the strongest deck ever. But hey, it could be worth a look.
The last card I saw was Avalugg. And this is another one of those ideas like the Swampert Mill deck I mentioned previously where I'm not sure how to run the deck optimally. His second attack can mill up to 9 cards if you can manage to mill 3 energies from yourself. So similarly to SpeedQuaza, you want to run a heavy energy count to try to mill as fast as possible. And milling anywhere from 3 to 9 cards from your opponent's deck per turn could be completely devastating against something like M Rayquaza which goes through it's deck so quickly with Shaymins. But there are a lot of problems with it. First of all, there's the same issue as with the Swampert Mill strategy I mentioned earlier in which you have to decide if you really need to run Palkia to get the energy, or if you're better not sacrificing those slots and instead relying on Max Elixir to get the 3 water on Avalugg. Then you also need to keep it going. You have to mill multiple times to deck out your opponent, and at Avalugg's 120 HP (160 with FFB) it isn't exactly taking hits well, so you will need to constantly be able to power one up quickly to answer the KO. Of course it does have some pros, such as being only a stage 1, not being an EX, being searchable with Heavy Ball, and having optional energy denial in its first attack. And to overcome the issue of having to get multiple stage 1's out, you could run Mew to use his attack since its a basic instead. So this is another card I'm not so sure about as a partner for Palkia, or whether it is better as its own standalone budget deck, or if it just straight up is not good enough for the format.