When I first saw Bristling Hydra there hadn't been any energy cards revealed, so I was evaluating it in a vacuum. I formed the opinion that it stands well enough on its own to be playable. It generates enough energy to enable its own ability, so it can be immediately be cashed in to create a 5/4, which is a competitive size for a four mana creature.
Alternatively, its Energy can be saved for an on-demand hexproof activation, the value of which is apparent against any opponent playing creature removal which is just about everybody. A creature with a built-in one-time protection ability against opposing answers is valuable in the context of cards like Declaration in Stone, Reflector Mage and the new Chandra, Torch of Defiance. While Bristing Hydra isn't a bonafide hexproof creature, even this one instance of protection creates a buffer that makes it difficult for opponents to find an answer.
I also figured that most of the value in Bristling Hydra would be in its synergy with other energy cards. Bristling Hydra can expend energy for extra +1/+1 counters and hexproof activations, which will prove useful over the game against an opponent relying on creature removal. I'm even more excited about Bristing Hydra's ability to enable other energy cards, which will dictate just how valuable Bristling Hydra and its three energy truly are. All energy sources and outlets will be worth looking at, and luckily there have now been some revealed that we can view next to Bristling Hydra.
Longtusk Cub is an ideal card to accompany Bristling Hydra in an aggressive energy deck. Assuming it can connect each turn, it will inevitably generate more Energy than other cards that only generate it when they come into play. It can be used to accumulate energy, which combined with Bristling Hydra and other energy cards will allow a deck to reach a big payoff.
It's also an outlet for Energy, and in terms of adding +1/+1 counters it is more efficient than Bristling Hydra so it's a great energy dump. The bigger it gets, more likely it will be able to connect and generate more, so aggressive plays on curve (like Bristling Hydra) will help to get more mileage out of Longtusk Cub.
Dipping into Red provides access to another aggressive energy-centric two-drop, Voltaic Brawler. Brawler excels because, unlike Longtusk Cub, it generates an immediate dose of energy. This means it effectively generates value even when immediately destroyed, so it's a premier creature that will be a staple in energy decks alongside Bristling Hydra. It starts hitting hard and fast, but because it doesn't generate additional Energy of its own it requires sources to keep it going. It will also be useful for simply accumulating and saving energy, whether it be for building an extra Hexproof activation for Bristling Hydra or a bigger payoff.
With a pseudo landfall trigger, Architect of the Untamed draws some comparison to Tireless Tracker, generating energy instead of a Clue token. Rather than growing itself, it can expend eight energy to create a 6/6 creature token. That's a lot of energy, and it will require sources like Bristling Hydra to function. Imagine a curve of Woodweaver's Puzzleknot into Architect of the Untamed into a land and Bristling Hydra, followed by a land the next turn: That's what it will take to achieve the eight energy required. Whether or not the card is constructed playable will depend on what other support it has, and a card like Bristling Hydra goes a long way.
Lathnu Hellion is designed to be an extremely hard-hitting and fast source of damage that soon leaves play as the newest incarnation of Ball Lightning. It generates enough energy to stick around for another turn and get a second attack so it's quite powerful on its own, but it can be broken if supported by additional sources of energy. Bristling Hydra is a perfect follow-up to Lathnu Hellion on curve, keeping it alive for yet another turn and getting halfway towards the next turn—if the opponent is even alive by then.
Another options is Territorial Gorger. Small for its cost, it takes generating an energy each turn to turn it into a very reasonable threat. Producing multiple in a turn makes it overpowered. It goes very well with Architect of the Untamed—just play your land for the turn—and it's further powered by aggressive energy sources like Bristling Hydra.
Multiform Wonder is a great source of energy and an even better outlet. Its ideal mode is a 5/1 Flying Lifelink, which requires three energy so Bristling Hydra an ideal enabler. The three Energy generated by Multiform Wanderer could also be used to activate Bristling Hydra, so the synergy goes both ways. A curve of Bristling Hydra into Multiform Hydra leaves the opponent in a difficult position. Multiform Wonder looks to have all the makings of a Standard creature, because in a deck with the right support it will consistently connect at full capacity.
Harness Lightning both generates energy and converts it into damage on a creature, so it's going to be excellent removal in an energy-centric deck. Adding three energy makes it something like a Lightning Strike on its own, but it will be able to take down larger creatures when powered by something like Bristling Hydra. It's also effective as an energy source since it can destroy a one or two toughness creature and leave some energy behind. It can also simply be used to add three energy if there is a creature in play to target, which means in a pinch it can create a surprise three energy to activate Bristling Hydra's hexproof!
Woodweaver's Puzzleknot works well for supporting Bristling Hydra, providing an extra hexproof activation and the ability to provide another. Any green deck that is hungry for energy is likely to include both of these cards, so their interaction will be an important feature of future Standard.
How might a deck using Bristling Hydra and taking advantage of other other Energy cards look? Something like this:
Bristling Hydra stands well on its own, especially in a Standard metagame saturated with creature removal. It excels when combined with other energy cards, which it feeds off with its own activated ability and enables in its role as an energy source. There have already been some excellent energy cards revealed so it's clear that Bristling Hydra will earn a place in Standard. I'm looking forward to seeing what other energy cards are printed that will make Bristling Hydra even better. What do you think about Bristling Hydra?