The card is still a value machine and as long as Black decks can fill their trash with characters with powerful on-play abilities, Gecko Moria will continue to rule the top end for the black color
Like most Magic: The Gathering cards, the value of Tribal Unity depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Planechase)
Its actually the same effect, but you get a 1/1 frog instead of the full creature
If both targets are illegal, Beat a Path will be put into its owner's graveyard
If you just want to stomp the game I think things are easiest with Squirtle and friends by far, since you can build it into a Rain Dance deck later and have something that's out of any of the CPU trainers' league, whereas Charizard and Venusaur aren't as competitively powerful(though Pokemon Center cheese with Venusaur is pretty entertaining...), but you can really get away with doing a decent version of whatever you feel like running so I'd just go with whatever you think sounds fun