Inv is a great general purpose tank with strengths in the S/L damage type and weakness to heavy psi damage. On teams, put your tank in the middle of the enemy mob and have Invincibility on. Then concentrate your damage on the Bosses. If there are no bosses, kill the lts. This tank is great for normal missions and Tanking most AVs (and even PvP), This tank is no so great for farming bosses in AE nor is it great on low damage teams. Its does not solo so well under level 40.
They work okay together. There isn't any 'synergy' that makes it a good combination, but there also aren't any conflicts that make it a combo to be avoided. My first tank was inv/EM and I took him to 50 and still use him for tough content.
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I dont have much experience with Inv, not past low teens anyway, plenty with EM, so I wonder how this works as a tanker. Give that my one AOE kinda sucks, should I just make him a Single-Target type guy? Keep em whacking on him and just energy punch one perp at a time?