I think early game the dogs that apply Scarlett rot are also really strong, can solo the first 3 bosses once levelled up!The best summons are the Mimic (more so if you are levelled up and kitted out), Tiche and there is a pair that can revive themselves which could be skeletons but I cant remember. There are cool little extras for the mimic like a talisman that aggros so once you summon him, unequip it and he takes all the damage while you plug away. Level 10 mimic for me now at level 222 with full access to all the best spells in the game and dual bloodfang is just ridiculous