Bit of an old post but i wanted to find out more about Carrion creepers and found an excellent post on it on US sites.Thought it would be of use to anyone thinking of going Plant dom.
Carrion Creepers (pet summon, AoE slow, knockdown, immobilise + small damage over time)
Available: level 26
Carrion Creepers is a wonderful power, and a truly unique beast in the CoH/V world - and rather difficult to describe. When you cast it (by choosing a location like any other pet power - although this can be cast very far away), a patch of dark brambles spread out in a large patch on the ground to indicate the radius of the power. These brambles are actually just graphical 'icing' to show where the power was initially cast - the actual power is an invisible untargetable pet which will actually follow you around when the mobs you cast it near are defeated (you can see it following you if you summon it and then walk through some water somewhere as you see a second set of ripples moving close behind you) - it will even follow you up elevators and it flies too so can keep up with you wherever you go. This invisible entity has a large slow aura around it which will slow the movement of any mobs near it and also has a -fly, -jump component. This makes it a particualrly vicious weapon in PvP as opponents won't even be able to see that you effectively have a huge slow, -fly, -jump aura following you around which will then stick to them like glue.
The invisible pet summons 'subpets' of its own (the huge creeper vines which spring up out of the ground and last just a short while) which attack the mobs close by. It will try to summon a creeper vine for each nearby enemy, but it does an accuracy check to decide whether each summon is successful or not - so slotting accuracy in this power will mean you get more creeper vine spawns - very noticeable in large teams. These creeper vines use a damage over time attack and have a chance to knock down too. When an enemy is defeated within range of the pet, a small patch of immobilising roots sprouts up which will entangle any nearby mobs, together with another creeper vine which begins attacking any nearby enemies too.
One of the key features of the power is the creeper vine 'subpets' - since they are actual physical entities which can be attacked by the mobs, the patch and its creepers actually absorb aggro which can make it an excellent move to open with (especially for absorbing large and dangerous 'alpha strikes'), allowing you to then move in with seeds of confusion. The aggro isn't always assured though so beware of some stray shots coming your way. It can be cast from around corners and behind obstacles though which can add even more safety. Beware of the range of the pet though - it can summon creepers quite a long way away which can be a risk when trying to avoid aggroing extra nearby groups of mobs.
It does eventually expire and it also has a very long recharge, so you will want to slot it with 3 recharges at the very least. I would also recommend 1-2 accuracies and then perhaps damage if you have any slots left over. Immobilise and slows are only of limited use really since the creeper vines attract aggro anyway so mobs aren't likely to try and run away. If you PvP then slows are perhaps of more value.
This is by far the best description i have been able to find on it and it explains the wierd stuff i have seen and was considering Bug reporting.