The Tavern

What: An evokable that summons 6 hostile howler monkeys, as close as possible to the player.

Why: Meat shields that will reliably block LOS in all directions, at the price of blocking a retreat and making noise. Could be an interesting mechanic.

If "as close as possible" means directly adjacent when no enemies are close enough, this would have a lot of abuse potential. Using your idea of blocking a retreat, an upstairs/ downstairs/ shaft can have at most 8 floor tiles around it. Using this new item, you could in the best scenario block 3/4 of possible tiles for enemies to step onto, at worst you could completely stop other advancing enemies and run away safely. Another immediate way to abuse this item would be to combine it with Ignition, which gets much more powerful depending on the number and placement of enemy targets.

These are just ideas off the top of my head, I'm sure other players could work out more ways to screw with existing game mechanics. If it makes any difference, I'm against this item being introduced.

While I am not in favor of adding this item, I can't imagine that using it to get more damage out of a level 8 spell is a serious balance concern.

In a 1vs1, it would be easy to deliver three to six fireballs at once with extra targets for the price of activation. Against several enemies at once, creating weak new enemies would abuse anti friendly fire AI, and also provide increased damage. Ignition is already meant for fighting groups of enemies. Damage aside, summoning hostiles at will to break line of fire is trouble. If I can spend 10 auts and no other resources whatsoever to change an encounter into something that benefits me with both damage output, and artificial blockers - yes, I think it's a balance concern.

Edit: the problem could be mitigated by making the item limited through charges or a cooldown of some kind. Even so, the interactions with enemy AI would be flawed by design imo.