This is one of my favorites. I would actually be quite interested in seeing this hero in action.
Q is an AOE that can be single targeted. Think Luna ult with Aghanims. There is no difference in effect when the ability is single targeted, it still hits both allies and enemies and either heals or damages them. It does get blocked by Linkens and transfered via the E when single targeted.
This is a nice simple ability that can be used for a quick burst of damage/healing. The W turns it into a soft disable as well. This spell has "dream" potential: You hit 5 enemies and 5 allies with it all at once. That's a good, fun feeling to have. At any moment players will be eveluating if they rather keep the spell until the perfect moment or throw it now to get some value.
W is a bit odd. Currently it will apply an effect to allied heroes around the Spellbender when they are hit by a spell. In of itself that isn't a problem but what exactly is defined as a spell? Does Sven cleave count as a spell? Should it? I'm unsure. I suppose a simple solution would be to say that passives don't count. Do items? They probably shouldn't. A simplified version of this ability would be "enemies that take magic damage are slowed" but that isn't as interesting and loses the allied dynamic.
While this ability creates some questions (to which I think the answers are "no passives or items") I do think it's a really interesting spell that's well suited for the hero.
E is beautifully absurd. It works on all spells that would be blocked by Linkens Sphere or reflected by Lotus Orb. I'll be referring to the hero 1 as the "transmitter" and hero 2 as the "receiver". There are a million ways to use it and all of them are quite silly. Redirect spells from an ally tramsitter to an ally receiver who carries Blademail and Lotus Orb to then bounce them back to the enemy that had cast them. Use it on your initator and then place the receiver on an enemy hero, making their team ruin their own hero.
It might be interesting to split the spell into two separate spells that are leveled up simultaneously. The first spell places the transmitter, the second the receiver. As the spell is currently described the transmitter always has to be placed first, which makes it a bit clunky. At the same time it's an interesting limitation and might be a lot more balanced.
Either way there has to be a limited time period for when the transmitter or receiver can be placed after the other has been placed. It would work like this: Place either one, the ability is active. Now you have 5s to place the other one, then the ability goes on cooldown.
The ability certainly couldn't have a long cast range or duration (maybe 8s at absolute most). It's something to be used for short fantastic plays, not for extended ones.
R might be a bit broken with a hard dispell. If it is, it could be changed to a soft dispell. It's a nice spell to trigger the passive, it can be transmitted with the E. It's definitely not supposed to be a high impact ultimate but instead a tool to constantly poke and annoy with. Currently there aren't very many purging effects in Dota, so adding an additional one is definitely not a bad idea either.
Overall I'm very happy with this hero. The Spellbender seems quite fun. Likely more of a support but I can see a core role happening as well. Would be a cool hero in both OAA and regular Dota.