[Ryastar]

Mostly agree with the above, as far as most of those being less useful spells, except for a few notable exceptions:

Pygmy is one of the best spells in the game. At level three it essentially kills 40% of the target stack, regardless of the size of it, for the duration of the spell. That's your chance to kill it. Think of it as soul drain for mages, costing mana (and at only 20, it's a steal), and sadly not usable on level 5 units.

Helplessness is also rather powerful. It reduces enemy defense by 60%. It's at its most powerful against level 5 units, making their impressive defense pitiful.

Those are two specific example, but also one thing in general, no spell is useless, it all depends on your playstyle. For example, Razorflame, you mentioned weakness, a spell I consider crap, as better than pygmy. My philosophy is that a dead enemy does no damage (unless it's UNdead, haha), so why bother reducing their damage when I can kill the stack instead, or in the case of pygmy, reduce their damage AND their hitpoints. See, it all depends on your strategy. Eg. the main use of kamikaze is on your own phantom troops, when their duration runs out, BOOM!!! I've also heard that despite the description, you can cast it on enemy troops as well. Invisibility allows for a cheap strategy, which I never use but you can find described somewhere on this forum. The basic idea is to have only one stack of troops (usually green dragons for mana regen), cast invisibility on them. Now they cannot be attacked by enemy troops unless they have the ability eyeless (thorns are the only ones with it, I believe) or by spells from the enemy hero, if any.