Two parts.
The reinforcements. In your Command phase in each of a set of battle rounds fixed by battle size, add a new POXWALKERS unit with a Starting Strength of 10 to your army, in Strategic Reserves. The rounds are 2 and 3 at Incursion, 2 to 4 at Strike Force, and 2 to 5 at Onslaught.
The keyword. POXWALKERS units from your army gain the BATTLELINE keyword.
At a standard Strike Force game that is three extra ten-model units, thirty free models, arriving across battle rounds two, three and four. In a faction whose problem is that it is slow and its aura is short, a stream of free bodies appearing behind the enemy's advance is a very different kind of pressure.
Read Strategic Reserves carefully, because that is the rule's real limitation. The units do not appear where you like; they arrive under the normal Strategic Reserves rules, from your table edge, on the turn you choose to bring them in. That is why the Hidden Amongst the Dead stratagem, which gives a reserve Poxwalkers unit Deep Strike, is the most important 1CP in the detachment, and why the Lord of the Walking Pox enhancement, which lets a reserve unit arrive as though it were the third battle round, is worth its 15 points.
At 2 DP it leaves 1 DP spare at a 2,000-point game.