Been fooling around with many Ter Adun decks lately and I must say that I like playing him quite a lot. It's true that he doesn't directly support your board control ambitions, but his asset is that he can deactivate a lot of drawing engines (bazaar, research and wizent's staff) which often leads to a greater strength in numbers on your side and forces the opponent to adopt a defensive stance if you manage to get past the first couple of turns.
This is the deck that, for me, works best so far:
1x Ter Adun
4x Fire Snake
4x Gargoyle
4x Keldor
3x Plasma Behemoth
4x Blood Frenzy
4x Valiant Defender
3x Warrior Training
1x Enrage
2x War Banner
Valiant Defender + Warrior Training can turn the tide even when going second against aggressive creature based decks, Amber and Gwenneth are put in a hurt locker that not even retreats can get them out of and if things go well the damage output of creatures + War Banner is high enough to defeat Elementalis. The deck has trouble dealing with board wipes, disspells (Jericho), Boris' Kill Gargoyle-ability and Wulven decks that use bad santas as drawing engine, but I haven't yet found a way for Ter Adun to avoid these weaknesses. Still there's no match-up he's an auto-loss against.
Specific strategies
Going First: Keldor is usually the stronger turn 3 option than gargoyle when you go first. Against humans it typically plays out like this: You drop a snake. They respond with Puwen, whom you scratch with your snake so that he has only 2 hitpoints left and send Keldor in. They play Jasmine or Aldon which you then kill with a pumped up Keldor. Puwen is left alone with 2 hitpoints and can hardly take the board from you.
Against shadow a snake scout is not so great as it will likely just get killed by a gargoyle. Against Majiya I play snakes anyway if I can since every measly hitpoint you take away from her might matter later on. Turns 3 & 4 play Keldor, then gargoyle. The 2 of them can even take out an enemy gargoyles during turn 5 (or Keldor does it by himself after you have played a War Banner).
When you're up against a mage Keldor is likely to get killed by a fireball and whether or not you want that depends on whether or not you have Blood Frenzy activated. If you have, a 1 for 1 card deal is in your favor even against Majiya, if not, play the gargoyle.
Nukes (Supernova, Tidal Wave): Fighting players with access to these cards is tricky since you can't just overwhelm them with one concentrated assault but rather need to send one wave of creatures after the other until your opponent runs out of ammo. By rule of thumb try to always be able to take out an Aeon and keep excess creatures as a reserve, even if you have nothing else to do with your resources. An unassisted Behemoth makes an excellent drop on an empty board and demands the next Tidal Wave or Supernova right away without having to take a card disadvantage (unless of course it gets webbed/frozen or retreated but that hasn't happened yet; mages and priests seem to not include these cards very often). Against priests make sure you have a War Banner out or on your hand, else drop a snake as assistance (Aeon rule).
Elementalis: I haven't mentioned Energy Discharge yet, which is a bit different than Nova and Tidal Wave. For one, you can – if at all – expect only 2 of them, not 4, and for two a lonely Behemoth is an open invitation to just mind control it. Placing one together with smaller creatures that could kill it if necessary isn't so bad though, esp. later on when a few MCs have already been used (Always keep count). Keep an eye on Elementalis' card and resource count just to make sure he won't be able to use Behemoth's ability the same turn it gets controlled. It doesn't really happen since you can shut down bazaar and often force them to burn low on 5 resources, but still.
Also, when dealing with mind control be careful when you use Valiant Defender – the property “Cannot be attacked” is carried over and some players know that and take advantage of it by not eating the creature immediately (since you can't kill it they can just as well let it attack for another turn). Soon as this bug is fixed VD will give Elementalis decks a pretty hard time I think. You could assign a fire snake as protector, leaving them to choose between taking over a bigger creature and not being able to attack with it or taking over the Snake Protector that then bites the hero for 1 damage (3 with shard out). If too much damage gets deflected on your hero then there's still Enrage.
Boris: The Problem here is that he can just kill your protector with his ability, so you need to get him to use it first. Assuming he goes first, he has 4 shadow energy after your 4th turn, meaning that his 2 & 3 drop will likely have killed your turn 3 creature, Boris will likely have used his ability to kill your next 3 drop (best to have a gargoyle for that one just to make him unwilling to do it with his creatures again) and *then* you can start turning tides by placing a Snake Protector and Valiant Defender and a Behemoth after that. So in short you need a pretty good starting hand and should pray he doesn't have shield bash or a few retreats ready. So yea Boris sucks for you. He breaks the backbone of shadow creature decks, gargoyles, just like that, but of course you don't go second and aren't confronted with a perfect starting hand all the time.
Why this and not that?
Mournblade: In theory it offers a way out of the dilemma that you can only play few creatures at a time against nuke decks, but after trying it for a while it turned out that it doesn't work often enough to warrant 1 or 2 of them in the deck. There are 2 reasons for this:
1. You have a hard time claiming board domination and placing a mournblade *during one turn*, which gives the other player time to respond before you have set the combo up. F.e. you might have snake and Keldor out with no enemy allies up against you, but to solidify your presence you need at least another 3 drop and then you often don't have the resources for the sword. Or you could need a plasma death bolt to get rid of Jasmine, which again leaves you with not enough resources.
2. 6 out of 8 heroes with nukes in their decks can have item destructs, too. (5 out 7 if you don't count Zaladar who doesn't benefit from having Energy Discharge on board.)
Valiant Defender over Crippling Blow: Both are merely tools that help take over the board. The difference is that CB takes out one creature's attack over the course of the entire battle while VD offers complete protection from attacks only during critical turns and I found that the latter is what you need much more often. Neither card prevents the use of ally abilities, but VD simply does a better job at keeping your allies in play which then take out abilities by killing the allies attached to it.
Keldor over Medusil: A good reason to choose Medusil is that you don't need resources to pump her up during your 4th turn which can instead consist of ability + another 3 drop or defender + protecor and from behind that screen she doesn't need to kill everything with one shot. Puwen can also be dealt with by Medusil without having to scratch him with your snake. But consider the going first example i've given further up with Medusil instead of Keldor: You play a snake. Puwen gets called out. You play Medusil and your snake attacks the hero. Puwen kills the snake and Jasmine gets played. If you don't have a War Banner ready by that point to increase Medusil's attack to 4 and kill Jasmine you're in bigger trouble than you would've been with Keldor.
War Banner over Bloodlust: Bloodlust is a short push aimed at removing enemy allies quickly before they can do damage, but you don't need it often when they can't attack anyway due to your weapon lock combo (except for Behemoth against which Bloodlust would be better suited). Over the course of a battle, War Banner adds more damage and few people remove it.
Alternatives
-3 Warrior Training
+3 Bloodlust
Matches are faster and the damage per creature is increased, which matters when you can have only a few of them out at a time (against nukers). Without protector you fall more easily prey to human aggro or elemental rush.
-2 War Banner
-3 Plasma Behemoth
+2 Dual Wield
+3 Berkerker's Edge
The job of your allies becomes to merely keep the board in check while you belabor the enemy hero with your berserker axes. Unlike with Amber and Gwenneth who straightaway tell their opponents “I'm gonna attack you with weapons” the other player will not as likely hold on to his or her item destructs against Ter Adun. Your typical weak spots don't go away however as you still need the board to set up weapon lock - without weapon lock and/or friendly allies the enemy allies just wear off your axes and force inefficient defensive strikes.
