Although there are characters that have five strength and could successfully challenge Jumba, his willpower is still high enough that he should be able to withstand a head-on challenge
If you look at the text, you can get this trigger from your attacks, too, which is wicked
While a 3/2 for four mana isnt great, the ability to counter a wide range of effects (spells, activated abilities and triggered abilities) or destroy a creature or planeswalker when Ertai enters makes this card an amazing Swiss Army knife that can answer a number of kill-on-sight threats, often in a surprising way, as the fact that this card counters triggered abilities can really stymy a foes game plan in unexpected ways
There are many ways to win with this in Commander, like pairing it with Demonic Consultation, and its the primary mover for Doomsday decks
Ill still analyze each color pair in its own right, but Id encourage drafters to keep an open mind about cards from outside their pair, even going into pack two and three