Normally a wizards mount can be on an arcane fulcrum but in the case of hte priest on a Stegadon, he also has several Skink crew. Can a skink priest with an EotG occupy an arcane fulcrum? Slann normally must deploy with Temple Guard and can't leave the Temple Guard. Does this prohibt a Slann occupying an arcane fulcrum if there is a unit of TG in the army?
The EotG (including the steggie and all its crew) can go on a fulcrum "as long as the model fits". It is a single model for the purposes of going on a fulcrum. The slann in a unit of Temple Guard is forbidden by the TG/slann special rules to leave TG and so cannot go on a fulcrum until all the TG unit is dead.