Ok, couple things.
1. Forest of Giant Plants is what makes DeciPlume work, not to mention level ball. And a lot of lists only play 4 DCE as their energy and play Tauros/Lugia as their Attackers.
2. My "Expensive" comment was about the energy costs. None of the other variants have an expensive cost, except Lapras, but that one has Max Elixer and Collect to compensate. T-Tar is two darks and a DCE for it's cost, which is three turns off energy attach MAYBE two with Mega Turbo.
3. Consistency is where the execution falls off. You need the mega line (4/3 with 4 spirit link) and Mega Turbo to get the mega built up. The reason Alakazam and Houndoom don't suffer from this problem AS much, is because of the two energy cost they have. Houndoom even has Blaze Energy to keep some of his energy on board. T-Tar needs too many things to attack turn two, and it's too hard to get multiple ones built quickly without dumping consistency cards in the deck list for more energy. Long story short: (2 Energy>4 Energy)
4. Mega Houndoom
80 Base (160 w/discard)
100 +1 Owl (180 w/discard
120 +2 Owls (200 w/discard)
140 +3 Owls (220 w/discard)