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Well, I've always been a proponent of Summoning for the Warlock, precisely because of the versatility of this school. Before version 3.0, I played as the Warlock because having the Trap skill from the start allowed me to quickly defeat large groups of powerful neutral creatures early in the game. And, accordingly, I also invested in Chaos (along with Summoning). But in the early stages, I only invested up to the Secrets of Chaos (for the powerful spell and Knowledge), as it was much easier to obtain them. By the way, I used Fist extensively in Utopias. Usually, people neglect the racial skill at the beginning, and the damage dealt by Black Dragons is simply laughable. But Fist can be both Empowered and Lucky, and it doesn't weaken.
And there's another trick in Summoning that few people use – Exorcism. It's fun to fight Demons with it. It gates Nightmares, and a Trap is placed where the gate was. When they appear, they immediately take double damage from 4 mines and then disappear... And it's also nice to one-shot an enemy Phoenix or Necromancer with a single cast...
Now I'm playing as Lethos. Darkness + Summoning is a really powerful combination. Even the simplest combination of Mass Slow + Fire Elementals is a very powerful thing. And I don't even need to talk about a Phoenix under Vampirism... It's a pity they removed Fire Wall from Summoning – it was a pretty good spell, very suitable for Trappers – the same principle as Plague. Cast it and watch as the guys in the fire wait and burn. And if you have both Plague and Wall...