Most likely (And this is what I would do) he'd block
consul's lieutenant because Drana, liberator of malikar only gives your creatures the power boost IF SHE deals damage successfully. If consul is able to
deal damage even once (say for instance by a trample effect) then your creatures will get +1/+1 stronger EVERY TIME they attack regardless of whether they all
deal damage or not. So with drana; creatures get stronger AFTER SHE deals damage. with consul; creatures get stronger even if he doesn't
deal damage (but only AFTER he becomes renowned).
Now looking at your scenario this is what I gathered (and I'm making the best out of this tricky situation so bare with me on this);
Drana, Liberator of Malakir (2/3) and
Consul's Lieutenant (2/1) are attacking (they both naturally have first strike) and
Mantis rider (3/3) blocks Consul.
Now if the damage goes on the stack (or in the order that I believe first strike damage goes) since it gives an extra combat step for those with FIRST STRIKE or DOUBLE STRIKE, both your creatures would hit at the same time and not one after the other, then the mantis will deal its damage to your lieutenant.
Since drana dealt damage, drana would become (3/4) the
consul's lieutenant would get a +1/+1 counter so he'd be (3/2). But since he already did his two points of damage,
mantis rider would still have 1 toughness left and would hit (because both the first strike effects happened at the same time and not one after the other) the extra 1 point of attack strength that the Consul's L receives won't be applied to any new damage for that phase.
So at the end of all that; Drana will be a (3/4) with first strike, the mantis would be
alive (because he only received 2 points of damage and not 3), and the Consul's L would be
dead because it only had 2 toughness (since he received the +1/+1 counter from Drana). Does this help clear things up?