I have not seen the Greenbond feat/template, or whatever its proper name is..
This is an interesting thought however, kinda like metamagic for summoning.
Thematically the templates should be ones that tie the summoned being more closely with the natural world as opposed to a dream world.. IMO, more solid/real
Change the feat to allow applying one of a listing of templates...
Perhaps templates named for the base elements, in a semi-druidic fashion.
Earthy (Strength ): As long as the creature remains in contact with the gound, it gains +4 to STR and DR 1/- per Hit Die of summoned creature. The creature also applies a -4 penalty to AC. Can only be used on land-based creatures.
{Visual description on evidently higher mass than a normal creature of the same type, moves a bit slowly but is strong.}
Water (Life ): Gains Improved Initiative and +10 to move speed. Natural weapons can critical undead due to the infusion of positive energy. The duration of the summoning spell is halved.
{visual description of swift and smooth movements, almost dancelike in nature. The creaure virtually glows with life.}
Fire (Rebirth ): Gains Fast Healing 1 and a +1D6 sneak attack per each 2 HD. The summoner takes lethal damage equal to 1 point per HD of the summoned being. {Must make a Concentration check to cast due to taking damage}
{Visual description on chaotic, almost beserker tactics and sudden deadly strikes}
Air (???? ): Gains immunity to criticals, Flight rating becomes Perfect, gains a +2 to hit while in flight.
{visual description on agility and difficulty to follow the quick, lightning like movements of the creature}
Anyway, these are just random thoughts and probably need alot of cleaning up before being allowed in public areas like the forum
