@ Propelled Rage
One thing up front: for the current playthrough I'd definitely follow Mike's advice and stick with Shapeshifter + Arcane Warrior. Perhaps Mike could open his bag of tricks and post some shapeshifting stunts you could pull in the Elven Ruins... I just don't have his experience in that field, the kind of experience that comes from going through thousands of encounters using a particular fighting style. My proficiency is more in the field of straight crowd control + nukeage, with a combined kill count of about 6000 across all playthroughs as CC/nuker. So I'm basically still a Padawan on the brink of becoming a full Jedi Knight.
Also those two spells that you get in warden's keep, how are they different from blood magic? I don't like Dark sustenance much
Those spells and abilities are based on the magic behind the darkspawn taint. Bloody Grasp can occasionally be useful because it does the same damage as Arcane Bolt against normal enemies and the same again over time against darkspawn. I rarely get around to using it, though. Perhaps one or two dozen times in a whole campaign. I'd rather give Avernus' potion to Leliana, but unfortunately that isn't possible.
Dark Sustenance is a sick joke, because it takes too long to cast for so little mana. Drop it from your quickbar and forget it even exists. Chugging a potion is three times as fast.
I run out of mana all the time, so does Morrigan or Wynn whenever they are in the team. Perhaps I've put one too many spells in the tactics slots.
You hit the nail on the head. The default tactics setups tend to ensure that your companions are always out of mana/stamina without accomplishing a whole lot. I heard that on some platforms you cannot control your companions directly, only indirectly via tactics. If that's the case on your console then you have no choice, but if you can control your companions then I'd jettison all of Morrigan's tactics except for emergency self-heal via Drain Life and perhaps emergency melee stoppage via Horror. Set her behaviour to "Ranged" to make her fire her staff at anything that moves without having to be told. Use her spells tactically.
You can let her use non-AoE spells like Lightning sparingly without blowing all of her mana by using a rule like "mana >= 50%" -> "goto XX" followed by "Enemy:Any" -> "Attack" and putting the spell rules after that. In this way you ensure that no mana goes to waste, but also that Morrigan will always have some mana if you need her to cast a tactical spell.
For Wynne, the best thing would be to google around for a nice healer setup or to look in the wiki. I could give only a few general pointers there because I use Wynne very rarely nowadays. Only for special fights like High Dragons, and then I set the tactics specifically for that fight. Needless to say, her behaviour should be set to "Ranged" as well to make her chip in with her staff.
As regards the Warden: your mana reserves will last longer and longer as you gain fighting experience (you, the player, not your toon), to the point where you won't need any mana refills at all outside of some boss fights and even there only a very small number of lesser potions. Lesser potions are the most cost-effective by far, and you can brew as many as you want at very little cost. My toons use only lesser potions and reserve all of the more powerful ones for rainy days, but the last time it actually rained in the past months was during the final boss fight in Golems of Amgarrak (but there it really poured, trust me).
I'm still working out (and loving) some spell combinations, so far I'm mainly using Sleep+horror & COC+stonefist and the improved drain, now going for the entropic death as I've heard it good too.
Ahhh, the mighty Cone of Cold. One of my favourite spells, especially when playing with a party. Cone + shatter + shatter + shatter + shatter. Four enemies dead. Five if Leliana has summoned a wolf or a bear. Doesn't work against undead, though, but they respond favourably to fiery treatments. With maxed spellpower, all it takes is a single Fireball.
Entropic Death is the biggest hammer there is, and a well-specced mage can one-hit even minor bosses with it. However, it is probably a luxury that you can ill afford. One way to make it affordable would be to have a companion learn Death Cloud, meaning that you have to spend only two extra points yourself on top of Vulnerability Hex and Affliction Hex to get the Death Hex. The first two hexes are bread-and-butter for any destructionist, comparable in importance to Cone of Cold, Fireball, the bomb spells and the first three glyphs.
Things you might want to try: freeze a bunch of enemies with Cone of Cold, inoculate the weakest of them with (Virulent) Walking Bomb, and then shatter the bugger or kill him with a suitable spell. Boom! One whole group of enemies dispatched.
Trickier but even more fun: if you see a cluster of enemies where one is on the brink of death, fire off a bomb spell. Instant detonation, instant wholesale destruction.
The boss killer: hex up the boss, then Walking Bomb, Virulent Walking Bomb and Crushing Prison, in that order. Watch his health race towards zero, while you throw Fireballs and other stuff on top of the mix.
The cowardly hexer: if you cast Force Field on a boss then you can hex him up at your leisure and finish off with a Paralysis Explosion when he gets out of it. Meanwhile, Morrigan can cast Inferno or Tempest or whatever.
The glyph shave: if you find yourself surrounded by loads of enemies, drop a Glyph of Repulsion on yourself. Should any enemies resist, treat them with Mind Blast and/or Cone of Cold. Run back a few metres and cast Glyph of Paralysis to set off a Paralysis Explosion. All enemies are now paralysed, giving you plenty of time to initiate any kind of treatment you deem appropriate.
The classic 'unfairness can be so much fun' combo: cast Glyph of Repulsion in a doorway, Inferno into the room. Spice up with hexes if necessary. Enemies who resist the glyph can be pushed back into the fire with Stone Fist or a well-placed Fireball. If loads of them seem to resist, throw an Earthquake into the mix. Works even with Ser Cauthrien (don't ask, you'll see when the time is right).
The glyph upgrade: if you have contained some enemies by way of a repulsion glyph, watch the little clock in the quickbar icon for the spell. If the enemies are still alive shortly before the glyph runs out, upgrade to a Paralysis Explosion by casting the paralysis glyph.
Corking the bottleneck: force-fielding your tank or an enemy in a doorway is a viable alternative to the repulsion glyph. If you have two Force Fields in the family then you can keep that hole plugged forever.
Anti-stealth measures: if you have to deal with invisible enemies, there are several options. If you hear the tell-tale sounds of cloaked genlocks or shrieks, open with Mind Blast and then drop a Glyph of Repulsion on yourself. You can 'probe' an area that may contain invisible enemies by flinging a Fireball into it or casting an AoE spell like Inferno; enemies that are hit become visible.
Playing cheese in a trap: if glyphs, Paralysis Explosion and Earthquake cannot keep your enemies in an Inferno long enough (e.g. bosses) then have your tank equip Wade's superior armour - or fire crystals, in the case of Shale - and have them run into the Inferno after grabbing the enemies' attention if necessary. Once in there, force-field your tank. Watch the bossy ogre beat and ram the force field ineffectually while he gets toasted. Works even better when soloing.
A note on spell placement: in most cases you will want to target Fireball at a fixed ground position rather than a moving enemy. You can use Fireball even in close-quarters combat as long as you take care to keep the edge of the AoE circle an inch away from your feet (i.e. your own melee circle). Paralysis Explosion is difficult to place precisely, but you can still paralyse someone who is standing right in front of you if you use the glyph's targetting circle as a measuring tool. The explosion will be centred on the second glyph you cast, with a radius of 7.5 metres. The glyph has a radius of 2.5 metres and a diameter of 5.0, meaning that the edge of the second glyph must be at least one glyph's diameter away from yourself.
Spells like Flame Blast and Cone of Cold can shoot through obstacles, like bookshelves and walls. Winter's Grasp, Drain Life, Crushing Prison, the glyphs and the hexes do not require line of sight. Dito for Inferno and its little brothers.