Griffon banner 8th edition empire warhammer magic standard overview
The griffon banner is a magic standard available for the empire in 8th edition warhammer with its substantial points cost it is only available to the armies battle standard. The griffon banner gives the unit carrying it double the rank bonus that it would normally has so at the maximum +3 for ranks the griffon banner would instead give +6 (and of course an extra +1 for the battle standard). This does however come at a cost the unit carrying the griffon banner cannot pursue enemy units and must always hold its ground when it breaks an enemy.
Very similar to the 7th edition incarnation of this magic banner the only main difference is a very minor points cost increase. Also is it the only " magical battle standard" left available to the empire with the demise of imperial standard (a battle standards hold your ground special rule now does the same at no extra cost) and the banner of Sigismund (granted stubborn but now in 8th edition steadfast kind of replaces this).
Pros and cons
Pros are that any extra static combat resolution is good as it makes you more likely to win combat thus giving you the chance to break units and avoiding your own units from having to take break tests. As you cannot pursue the griffon banner is most effective against vampire counts, tomb kings and daemons of chaos where the extra combat resolution means more kills and the inability to pursue makes no difference. A extra +3 to combat rsolution can make a lot of difference in close combats,
Cons are that not being able to pursue can cost you valuable victory points, there are ways round this (engaging with another unit that can pursue for example) but which entail extra effort to achieve. The fact it can only be taken by the battle standard is also a major issue, once your opponent realises this one model is giving you +7 static combat resolution (1 for battle standard, 6 for 3 ranks) they will no doubt make every attempt to kill them.
Also as the magic standard takes up all your magic item points allowance this leaves you relying on mundane armour to keep the captain alive. Whilst a 1+ save whilst mounted is readily achievable this can also cause problems as it is infantry that are most likely to have the required ranks for this banner to work most efficiently. This makes the battle standard a target for template weapons and spells or cause you to take him on foot so lowering his armour save and making him easier to kill.
The other downside of the griffon banner is that it requires ranks to be most effective, as the unit loses ranks it becomes less powerful as it effectively doubles your rank bonus, if you don't have any then there is nothing to double.