Deck Concept: 
has a lot of very good but very expensive minions, and in Gothic it got some very solid voidwalkers - These both have obvious synergyies with Harbinger, who helps make high cost cards a little more manageable to get out, & can take advantage of portals in the void for discounted voidwalkers. is also probably the element that benefits most from a mono-element approach, because you get to force an entire half of the board to be water, which is really useful for effects like or cards like or . Thematically this is all very appropriate for a of the deep, bringing forth a horde of sea monsters and elder gods like
Strategy: Unlike a lot of my decks, this deck is most comfortable taking its time - it is loaded up with tons of late game threats between its powerful and expensive minions, and the 2 sites. You don't have a lot of great tools to push the tempo early, but you should be able to defend yourself reasonably well between your early minions and magic, so as long as you make it to late game with some big threats in your hand you'll have a good chance of turning the tide! Because you're counting on getting to high mana cards, take even more care than usual not to let your opponent fence you off with their sites - I often draw more sites in playing this deck than my other ones to ramp slightly faster.
Weaknesses: This deck is definitely susceptible to getting run over if the other deck is really aggro - the other thing that can be a big problem for it is if your opponent is able to just kill your big threat monsters with smite, bury etc, instantly ending your late game comeback potential