So for a quck refresher the venomthrope statline is as follows: [M6" / T5 / Sv4+ / W3 / Ld8 / OC1] 70pts for a unit of 3 They have 5 attacks on an anti-infatry 2+ weapon.

A malanthrope in comparison is 75 pts and otherwise identical stats excepting 10 wounds and Ld7, it also has a garbage weapon of its own.

So why take a malanthrope instead of 3 more venomthropes? Well first of all it completely offsets its own weak attacks by giving the whole unit access to sustained-hits 1 and since anti-X weapons count as critical hits its immediately doubling the damage output of the acompanying venomthropes.

The malanthrope is also bringing synapse to the unit and increasing foul spores radius from 6" to 9". As a final advantage its 10 wounds are in one model, a normal unit of 6 venomthropes would lose effectiveness for every 3 wounds lost however a unit of 3 venomthropes with an attatched malanthrope can maintain full effectiveness for 9 wounds before damage output begins to fall.

Theoretically the benefits of a malanthrope only grow greater if attatched to a unit of 6 venomthropes as their fighting power would increase to that of 12 ordinary venomthropes for only 3/4 the cost.