Sure you'd rather start Trubbish or Thunder Wave than another non-starter, but that doesn't necessarily make it a starter, it makes it better to start with than your other Pokemon. As for the Tornadus donks, if tornadus active+dark mon benched+energy switch+dark patch+dark energy+way to get dark energy in the discard+DCE on the first turn is common in your meta, then the people in your meta are cheating, they're impossibly lucky, or we have very different definitions of common (or a combination). Sorry.
That's pretty below the belt concidering I play Darkrai/Tornadus/Bouffalant and have gotten first turn Power Blast and Gold Breaker. Before you call it cheating, play the deck, see how it runs, it's very fast and very easy to get Donks.
If I get two energy in the graveyard on my first turn then attaching to Manaphy gives me a 25% chance of getting 2 energy back, aka advantageous, 50% chance of getting 1 energy back, aka disadvantageous (same amount of energy on my intended mon as if I had attached to them, but with energy in the discard where I might have wanted to discard something else or nothing at all) and 25% chance of getting nothing, which is really bad. So yeah its not worth it if 75% of the time you're getting negative to neutral effect out of it.
Fisrt off, this is not Yu-Gi-Oh, there is no monsters or graveyard. Second, the Attack say you get three flips, garunteed, so that's three chances to get heads, which is a 33.3% chance of getting two energy and a 66.6% chance of getting one. While yes the 66.6% is the same as attaching to the intended POKEMON, it's not really worth the flip, but it's still worth the free card you get to search for. now, if you have two energy in the discard and you only get one one the first time around, that's great, because it becomes a win-win in your favor, you have another 66.6% chance of getting the other energy, or Manaphy gets KO'd, giving you a free card.
12 energy hardly guarantees that you'll get 3+ on the first turn as well as a Juniper and/or Ultra Ball. Anyway, now let's do some math. The chances of you getting 3 water energy (12/60 x 11/59 x 10/58), an ultra ball (x 4/57) and a manaphy, assuming you run 4 (x 4/56) in 8 cards, maybe 7 more with juniper is like 110/227563, but of course its actually worse than that because you have to get your draw supporter, and get the cards in the right order. You can also get 2 water+manaphy+juniper, a 704/487635 chance, but note that you'll need to draw into an ultra ball or keldeo either in that case. Even assuming you're running 4 Keldeo even though most decks would run 3, the chances of that are 3/77, totaling 2112/37547895 for the second scenario. Reducing both scenarios to 1/x and adding them together we get under 1/19847. Considering only a quarter of the time will either of those scenarios actually benefit you anyway because of the flippiness of Manaphy's attack and we're at 1/79388 (most likely less) or so games in which you'll be able to use Manaphy's attack to get a single energy on Keldeo that you would not have gotten otherwise, and in a deck that can attach all the energy in its hand as soon as it sets up a stage 2. Is 4 cards worth that? I don't think so. My math might be wrong somewhere along the way, feel free to point out if it is.
For my math, I got .21% for getting Manaphy (two copies) in your starting hand, a .388% chance of one water energy, a .476% for getting two, and a .327% of getting an Ultra Ball and Juinper (respectivly), how did I get these numbers, because it's the same numbers I came acrossed with Darkrai/Tornadus, now, these numbers may not seem promising, but it's a lot better than it looks, because all together, getting both energy back from the discard an all, (this took some math) you get a .274% of getting a perfect set up, so every one in four games with starting with Manaphy, now, while that doesn't seem pleasing, it's a 751% chance of getting one energy, so 3 out of 4 games. Now, that's starting with Manaphy which again is only a .21% chance, with 2 copies. So if you start with him, it it's great for you, if you don't, you now have 2 copies of Ultra Ball bait.
Except with Roserade you get the card when you want it. With Manaphy you get it when your opponent wants you to. Roserade is better.
Yes Roserade is better, that's not the point, the point is that getting a free card doesn't hurt, early or late game. You said the late card isn't worth it, a late game free search can help in any game. Also, your arguement to this topic actaully hurts your arguement to opening with Manaphy.
I for got to mention one thing, what if it's not a trainer you arelooking for with Manaphy's ability? What if it's a Supporter, or a Pokemon, or and energy, where's your Skyla then? Taking up space in your hand and in your deck.