First, I'm kinda bad with items. And with items, I mean costs and meaningful stats. Numbers Schnumbers therefore and don't forget everything is subject for change. For costs, I instead state the intended tier of the items.
Also, no "Item info"-template because I've seen how messy it can become with several items, even when tabs are included.
Stats: +20% Magic Resistance, +4 mana regeneration
Passive: The wielder gains +5% Movement Speed for 1 second whenever he or nearby allied heroes receive damage.
Bracelet of Divinity
Stats: +3 STR, +3 AGI, +3 INT
Basic Idea: Not only does this "abuse" the fact that the stats would still count as "a single ability", but this would also open up new ways for constructing Tier 2- and 3-items.
Stats: +25 AP, +10 INT
Active: Target tree turns into a loyal Treeling. The Treeling is controlable and sturdier than a melee minion, but not necessarily stronger and definitely slower. He doesn't have a lifespan, but will instantly die if he's too far away from the hero. Only a single Treeling can exist at the same time.
Basic Idea: Just a simple summoning item for squishy mages to support their midgame if they go solo-lane. The "maximum radius" is necessary so that they don't become a cheap vision-tool.
Stats: +25 AD, +30% AS, +500 Mana
Passive: After casting a spell, next attack within 10 seconds deals 120% base AD bonus physical damage and silences for 0.25 seconds.
Basic attacks restore youmana, doubled against enemy heroes.
Basic Idea: I always thought that BoM and EB would make a great pair if fused together, so here it is, a great late-game item against mages. If this would go above the 4 abilities-limit, then make the "after casting"-effect steal a good amount of mana instead of silencing.
Tier: 2 (relatively high cost for Tier 2, though, so "2.5" tier)
Stats: +50 AD, +180 HP
Passive: The wielder gets stunned for/ seconds whenever he attacks a hero or boss monster.
Basic Idea: A high-risk, high-reward item for melee attackers who don't rely too much on attack speed. The trigger can be changed to "when damaging" instead if needed (although that could be funny with Herculeon when he activates his ult: Perma-ministunned)
Soul of Nature
Active: Target tree gets destroyed, instantly healing the user for 80 health and another 80 health over 8 seconds.
Basic Idea: Tango-expy. 'nuff said
Stats: +250 health, +6 health regen
Passive: +8% Life Steal
Basic Idea: A more defensive Life Steal item. Of course it would make more sense to pair it with AD for more Life Steal, but this should be something that melee bruisers would like. It would also make a nice item for Tier 3-recipes.