Summon Monster: Starting at 1st level, a summoner can cast summon monster I as a spell-like ability a number of times per day equal to 3 + his Charisma modifier. Drawing upon this ability uses up the same power as the summoner uses to call his eidolon. As a result, he can only use this ability when his eidolon is not summoned. He can cast this spell as a standard action and the creatures remain for 1 minute per level (instead of 1 round per level). At 3rd level, and every 2 levels thereafter, the power of this ability increases by one spell level, allowing him to summon more powerful creatures (to a maximum of summon monster IX at 17th level). At 19th level, this ability can be used as gate or summon monster IX. If used as gate, the summoner must pay any required material components. A summoner cannot have more than one summon monster or gate spell active in this way at one time. If this ability is used again, any existing summon monster or gate immediately ends. These summon spells are considered to be part of his spell list for the purposes of spell trigger and spell completion items. In addition, he can expend uses of this ability to fufill the construction requirements of any magic item he creates, so long as he can use this ability to cast the required spell.
Fused Eidolon: A synthesist summons the essence of a powerful outsider to meld with his own being. The synthesist wears the eidolon like translucent, living armor. The eidolon mimics all of the synthesist’s movements, and the synthesist perceives through the eidolon’s senses and speaks through its voice, as the two are now one creature.
While fused with his eidolon, the synthesist uses the eidolon’s physical ability scores (Strength, Dexterity, and Constitution), but retains his own mental ability scores (Intelligence, Wisdom, and Charisma). The synthesist gains the eidolon’s hit points as temporary hit points. When these hit points reach 0, the eidolon is killed and sent back to its home plane. The synthesist uses the eidolon’s base attack bonus, and gains the eidolon’s armor and natural armor bonuses and modifiers to ability scores. The synthesist also gains access to the eidolon’s special abilities and the eidolon’s evolutions. The synthesist is still limited to the eidolon’s maximum number of natural attacks. The eidolon has no skills or feats of its own. The eidolon must be at least the same size as the synthesist. The eidolon must have limbs for the synthesist to cast spells with somatic components. The eidolon’s temporary hit points can be restored with the rejuvenate eidolon spell.
While fused, the synthesist loses the benefits of his armor. He counts as both his original type and as an outsider for any effect related to type, whichever is worse for the synthesist. Spells such as banishment or dismissal work normally on the eidolon, but the synthesist is unaffected. Neither the synthesist nor his eidolon can be targeted separately, as they are fused into one creature. The synthesist and eidolon cannot take separate actions. While fused with his eidolon, the synthesist can use all of his own abilities and gear, except for his armor. In all other cases, this ability functions as the summoner’s normal eidolon ability (for example, the synthesist cannot use his summon monster ability while the eidolon is present).
This ability replaces the class’s eidolon ability, bond senses, and life bond.
The following class abilities function differently for synthesist summoners.
Fused Link (Su): Starting at 1st level, the synthesist forms a close bond with his eidolon. Whenever the temporary hit points from his eidolon would be reduced to 0, the summoner can, as a free action, sacrifice any number of his own hit points. Each hit point sacrificed this way prevents 1 point of damage done to the eidolon (thus preventing the loss of the summoner’s temporary hit points), preventing the eidolon from being killed and sent back to its home plane.
This ability replaces life link.