While the general consensus is that it's fine as it is because mana production of this sort is a green mechanic, some people are still sold on the fact that it makes mana based on the number of enchantments out on your side, which has been done by Serra's Sanctum back in the Urza's Saga expansion
At casual tables, however, it might actually be too good
Theyre also the easiest to find in booster packs (being, as the name suggests, the most common type of card)
To make sure you have enough win conditions, Waste Not and Nyxathid come in
As unreliable as cascade can be sometimes, youre getting at least four cards for your trouble
Portal: Three Kingdoms (1999) had two spells