For the most part, trying to stay Dimir is ideal and lets you draft the necessary pieces for your deck when they show up, but on a draft-by-draft basis, you want to be aware of the reasons to go into additional colors
For example a 3/3 vanilla dork could normally block a 2/2 first strike and then slay it
Phyrexian Triniform is bonkers on that solo
80 land edh deck Land (87) 1x Blighted Cataract 1x Drownyard Temple 1x Geier Reach Sanitarium 78x Island 1x Magosi, the Waterveil 1x Mikokoro, Center of the Sea 1x Minamo, School at Water's Edge 1x Nephalia Academy 1x Reliquary Tower 1x Spawning Bed Planeswalker (1) Creature (4) Instant (4) Sorcery (3) Suggestions Updates Add Comments Attention
Equipoise (Block) On the surface, this enchantment seems more annoying than potent: you can never come out ahead plus the effects are only temporary
You can find interesting new ways to utilize drawbacks, provide better upsides, or make him an even bigger monstrosity