I was thinking Guardian as I read the OP too Those are good tactics for pretty much any mystic build. So if you are in healer, cleric, guardian, druid, reaver, paladin, the above strategy is how you play.
Guardian has skin like thornwood (+164 armor, 5% chance to deal damage to attackers), passive +162 slash/crush/pierce resists, +150 strength passive, +148 1hc +152 2hc passive, morning dew (small hot, +168 magic evasion). Downside can't wear plate, no intercepts or aura's for the group. Can use the mystic damaging spells. Can be a good "solo tank".
Paladin has aura of command(group buff of +123 attack skill against everything) -or- aura of light (group buff 50% incoming damage vs undead. 125% outgoing damage vs undead)(doesn't stack with aura of command), healing touch (100% heal on group member, 5 min recycle), blessing of life (5% self heal every 20 seconds). Wears plate and gets the mystic damage spells. If you are hunting undead this is the best tank (the 50% incoming dmg from undead is group buff).
Healer gets illustrius stand, a group buff that lowers incoming attack skill from undead, or the aura of health group hot (group buff 5% heal every 5 seconds for up to 85% heal, once a minute), plus more heals/ability heals. Gets all heal spells and mystic damage spells. Even just wearing the chainmail, this is the class my ped is pretty much always in, and he can take on multiple blight hounds and live. It's possible to tank as healer. Use druid spells to stun mobs that go after group members.
Cleric has area dispirit, which slows incoming attacks from all mobs it lands on, Protectorate (85% chance to intercept attacks directed at the group member), and aura of resistance(group buff +104 slash/crush/pierce resistance). Wears plate. Can use all the heal spells and mystic damage spells. For a small group this is a good tank.
Warrior has the most tank-like abilities: Defend Other (30% intercept chance on group member, lasts 15 minutes), Interpose (100% intercept chance for 20 seconds), Distract III (45% intercept chance for 2 minutes), Shield stance (+20 block bonus). wears plate, but can't use mystic spells (for damage/stuns/lifetaps), only gets the revits for healing. So if you use this class to tank, you will need someone healing you. To effectively play this as a tank you need to know all the abilities inside and out.
Battlemage gets shimmer field (+20 block, +20 parry), defend magic (30% chance to intercept spells directed to the group member, 15 minutes), but no other damage intercepters and can only use revits. Wears plate and can use arcane spells like daunting mist (slows movement and attack speed), plus the arcane bombs and ice roots. Rounding up a group mobs, get them tight on you, slow them with daunting mist, run out, then flame,ice,energy bomb them and you just killed a bunch of mobs fast (can be good exp). Get a group member to throw heals on you. Good for group leveling hunts but the group members need to be on their toes. I leveled many levels this way when in arcane schools. It can be tricky but its fun.
Another import thing to consider for a tank build would be the race. Sslisk gets sslisk regen, a full heal over time. Dwarves get dwarven toughness (temporary full damage immunity). One of those 2 would be best for tanking.
And as far as tanking the epics goes, you'd want to be in plate for sure. Epics have abilites which counteract many of the class abilities, such as banish armor immunity, stun immunity, dispirit immunity, mezz immunity... So you want lots of armor and heals, and can pick the one that's right for the job.