I love playing the fire splinter as well. In the smaller mana matches Antoid Platoon is a great tank. Almost half the cost of Living Lava, the same armor a shield ability. It has less attack, but in a smaller mana match it tends to hold up long enough to take out the opponents.
The Monk can also be a solid choice with his regeneration and only 4 mana cost :)
The heatsmith can and scavo chemist can also make half decent roadblocks if the mana is really tight.